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| motorola, 1996 all rights reserved. motorola reserves the right to make changes without further notice to any products herein. motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. "typical" parameters can and do vary in different applications. all operating parameters, including "typicals" must be validated for each customer application by customer's technical experts. motorola does not convey any license under its patent rights nor the rights of others. motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the motorola product could create a situation where personal injury or death may occur. should buyer purchase or use motorola products for any such unintended or unauthorized application, buyer shall indemnify and hold motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that motorola was negligent regarding the design or manufacture of the part. motorola and are registered trademarks of motorola, inc. motorola, inc. is an equal opportunity/affirmative action employer. mc68hc681 dual asynchronous receiver/transmitter (duart)
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(310) 594-4631 motorola mc68hc681 user? manual v table of contents paragraph page number title number section 1 introduction 1.1 internal control logic ........................................................................... 1-4 1.2 timing logic ......................................................................................... 1-4 1.3 interrupt control logic.......................................................................... 1-5 1.4 data bus buffer .................................................................................... 1-5 1.5 communication channels a and b ...................................................... 1-5 1.6 input port.............................................................................................. 1-5 1.7 output port ........................................................................................... 1-6 section 2 signal descriptions 2.1 v cc and gnd ....................................................................................... 2-2 2.2 crystal input or external clock (x1).................................................. 2-2 2.3 crystal input (x2) ................................................................................. 2-3 2.4 reset (reset ) .................................................................................. 2-3 2.5 chip-select (cs ) .................................................................................. 2-3 2.6 read/write (r/w ) ................................................................................. 2-3 2.7 data transfer ackowledge (dtack ) ................................................... 2-4 2.8 register-select bus (rs1?s4) .......................................................... 2-4 2.9 data bus (d0?7) ................................................................................ 2-4 2.10 interupt request (irq ) ......................................................................... 2-4 2.11 interupt ackowledge (iack ) ................................................................. 2-4 2.12 channel a/b transmitter serial-data output (txda/txdb)................. 2-4 2.13 channel a/b receiver serial-data input (rxda/rxdb)....................... 2-4 2.14 parallel inputs (ip0?p5) ...................................................................... 2-4 2.14.1 ip0 .............................................................................................. 2-4 2.14.2 ip1 .............................................................................................. 2-5 2.14.3 ip2 .............................................................................................. 2-5 2.14.4 ip3 .............................................................................................. 2-5 2.14.5 ip4 .............................................................................................. 2-5 2.14.6 ip5 .............................................................................................. 2-5 2.15 parallel outputs (op0?p7) ................................................................ 2-5 2.15.1 op0 ............................................................................................ 2-5 2.15.2 op1 ............................................................................................ 2-5 2.15.3 op2 ............................................................................................ 2-6 2.15.4 op3 ............................................................................................ 2-6 table of contents (continued) paragraph page number title number vi mc68hc681 user? manual motorola 2.15.5 op4 ............................................................................................ 2-6 2.15.6 op5 ............................................................................................ 2-6 2.15.7 op6 ............................................................................................ 2-6 2.15.8 op7 ............................................................................................ 2-6 section 3 operation 3.1 transmitter ........................................................................................... 3-1 3.2 receiver ............................................................................................... 3-2 3.3 looping modes..................................................................................... 3-4 3.3.1 automatic-echo mode................................................................ 3-5 3.3.2 local-loopback mode................................................................ 3-5 3.3.3 remote-loopback mode............................................................ 3-5 3.4 multidrop mode .................................................................................... 3-5 3.5 counter/timer ...................................................................................... 3-6 3.5.1 counter mode ............................................................................ 3-6 3.5.2 timer mode ................................................................................ 3-7 section 4 programming and register descriptions 4.1 programming descriptions................................................................... 4-1 4.2 register bit formats ............................................................................ 4-6 4.3 register description........................................................................... 4-13 4.3.1 channel a mode register 1 (mr1a)........................................ 4-13 4.3.1.1 channel a receiver ready-to-receive control ?mr1a[7]. ..................................................... 4-13 4.3.1.2 channel a receiver-interrupt select - mr1a[6]........... 4-13 4.3.1.3 channel a error mode select - mr1a[5]...................... 4-13 4.3.1.4 channel a parity mode select - mr1a[4:3]. ................ 4-13 4.3.1.5 channel a parity type select - mr1a[2]. .................... 4-13 4.3.1.6 channel a bits-per-character select - mr1a[1:0]........ 4-13 4.3.2 channel a mode register 2 (mr2a)........................................ 4-14 4.3.2.1 channel a mode select - mr2a[7:6]............................ 4-14 4.3.2.2 channel a transmitter request-to-send control - mr2a[5]. ........................................................ 4-15 4.3.2.3 channel a clear-to-send control - mr2a[4]................ 4-16 4.3.2.4 channel a stop bit length select - mr2a[3:2]. ........... 4-16 4.3.3 channel b mode register 1 (mr1b)........................................ 4-16 4.3.4 channel b mode register 2 (mr2b)........................................ 4-16 4.3.5 channel a clock-select register (csra) ............................... 4-16 table of contents (continued) paragraph page number title number motorola mc68hc681 user? manual vii 4.3.5.1 channel a receiver clock select - csra[7:4]............. 4-16 4.3.5.2 channel a transmitter clock select - csra[3:0]......... 4-16 4.3.6 channel b clock-select register (csrb)................................ 4-17 4.3.6.1 channel b receiver clock select - csrb[7:4]............. 4-17 4.3.6.2 channel b transmitter clock select - csrb[3:0]......... 4-17 4.3.7 channel a command register (cra)...................................... 4-17 4.3.7.1 cra[7]. ......................................................................... 4-17 4.3.7.2 channel a miscellaneous commands - cra[6:4]. ....... 4-17 4.3.7.3 channel a transmitter commands - cra[3:2]............. 4-18 4.3.7.4 channel a receiver commands - cra[1:0]................. 4-18 4.3.8 channel b command register (crb)...................................... 4-19 4.3.9 channel a status register (sra) ............................................ 4-19 4.3.9.1 channel a received break - sra[7]. ........................... 4-19 4.3.9.2 channel a framing error - sra[6]. .............................. 4-19 4.3.9.3 channel a parity error - sra[5]. .................................. 4-19 4.3.9.4 channel a overrun error - sra[4]. .............................. 4-19 4.3.9.5 channel a transmitter empty - sra[3]. ....................... 4-19 4.3.9.6 channel a transmitter ready - sra[2]........................ 4-20 4.3.9.7 channel a fifo full - sra[1]. ..................................... 4-20 4.3.9.8 channel a receiver ready - sra[0]............................ 4-20 4.3.10 channel b status register (srb) ............................................ 4-20 4.3.11 output port configuration register (opcr) ............................ 4-20 4.3.11.1 op7 output select - opcr[7]. ..................................... 4-20 4.3.11.2 op6 output select - opcr[6]. ..................................... 4-20 4.3.11.3 op5 output select - opcr[5]. ..................................... 4-20 4.3.11.4 op4 output select - opcr[4]. ..................................... 4-20 4.3.11.5 op3 output select - opcr[3:2]. .................................. 4-21 4.3.11.6 op2 output select - opcr[1:0]. .................................. 4-21 4.3.12 output port register - opr[7:0]............................................... 4-21 4.3.13 auxiliary control register (acr).............................................. 4-21 4.3.13.1 baud-rate generator set select - acr[7]. .................. 4-21 4.3.13.2 counter/timer mode and clock source select ?acr[6:4]. .......................................................4-22 4.3.13.3 ip3, ip2, ip1, and ip0 change-of-state interrupt enable ?acr[3:0]. .....................................................4-22 4.3.14 input port change register (ipcr).......................................... 4-22 4.3.14.1 ip3, ip2, ip1, and ip0 change of state - ipcr[7:4]. .... 4-22 4.3.14.2 ip31 ip2f ip1, and ip0 current state ?ipcr[3:0]. .... 4-22 4.3.15 interrupt status register (isr) ................................................. 4-22 4.3.15.1 input port change status - isr[7]. .............................. 4-23 4.3.15.2 channel b change in break ?isr[6].......................... 4-23 4.3.15.3 channel b receiver ready or fifo full ?isr[5]....... 4-23 table of contents (continued) paragraph page number title number viii mc68hc681 user? manual motorola 4.3.15.4 channel b transmitter ready ?isr[4]....................... 4-23 4.3.15.5 counter/timer ready ?isr[3].................................... 4-23 4.3.15.6 channel a change in break ?isr[2]. ........................ 4-23 4.3.15.7 channel a receiver ready or fifo full ?isr[1]. ..... 4-23 4.3.15.8 channel a transmitter ready ?isr[0]....................... 4-23 4.3.16 interrupt mask register (imr).................................................. 4-23 4.3.17 count registers (cur and clr) ............................................. 4-24 4.3.18 counter/timer preload registers (ctur and ctlr).............. 4-24 4.3.19 interrupt vector register (ivr)................................................. 4-24 section 5 electrical specifications 5.1 absolute maximum ratings ................................................................. 5-1 5.2 thermal characteristics ....................................................................... 5-1 5.3 power considerations .......................................................................... 5-1 5.4 dc electrical characteristics................................................................ 5-2 5.5 ac electrical characteristics................................................................ 5-3 5.5.1 clock timing .............................................................................. 5-3 5.5.2 reset timing ........................................................................... 5-4 5.5.3 read and write bus cycle timing ............................................. 5-4 5.5.4 interrupt bus cycle timing......................................................... 5-5 5.5.5 port timing................................................................................. 5-7 5.5.6 interrupt reset timing................................................................ 5-8 5.5.7 transmitter timing ..................................................................... 5-8 5.5.8 receiver timing ......................................................................... 5-9 5.5.9 transmit and receive operation ............................................. 5-10 section 6 mechanical data and ordering information 6.1 pin assignments .................................................................................. 6-1 6.2 ordering information ............................................................................ 6-1 6.3 package dimensions ........................................................................... 6-2 6.4 pin assignment?0 pin dual-in-line plastic package.......................... 6-3 6.5 ordering information ............................................................................. 6-3 6.6 package dimensions?0 pin dual-in-line package............................. 6-4 table of contents (continued) paragraph page number title number motorola mc68hc681 user? manual ix appendix a MC68HC2681 a.1 introduction ......................................................................................... a-1 a.1.1 interrupt control logic.............................................................. a-1 a.1.2 input port.................................................................................. a-1 a.2 signal description ................................................................................ a-1 a.2.1 reset (reset )......................................................................... a-4 a.2.2 chip-select (cs ) ...................................................................... a-4 a.2.3 write strobe (w )....................................................................... a-4 a.2.4 read strobe (r) ....................................................................... a-4 a.2.5 parallel input 6 (ip6)................................................................. a-4 a.2.6 parallel input 2 (ip2)................................................................. a-4 a.3 programming and register description .............................................. a-4 a.4 electrical specifications ...................................................................... a-6 a.4.1 absolute maximum ratings...................................................... a-6 a.4.2 thermal characteristics ........................................................... a-6 a.4.3 dc electrical characteristics.................................................... a-6 a.4.4 ac electrical characteristics .................................................... a-7 a.4.4.1 clock timing ................................................................. a-7 a.4.4.2 reset timing .............................................................. a-8 a.4.4.3 bus timing..................................................................... a-8 a.4.4.4 port timing ................................................................... a-9 a.4.4.5 interrupt reset timing ................................................. a-9 a.4.4.6 transmitter timing....................................................... a-10 a.4.4.7 receiver timing.......................................................... a-10 a.5 mechanical data and ordering information ....................................... a-14 a.5.1 pin assignment?4 pin plastic leaded chip carrier.............. a-14 a.5.2 fn suffix ordering information................................................. a-14 a.5.3 fn suffix packaging dimensions ............................................. a-15 a.5.4 pin assignment?0 pin dual-in line plastic package............ a-16 a.5.5 p suffix ordering information ................................................... a-16 a.5.6 packaging dimensions?lastic............................................... a-17 index table of contents (continued) paragraph page number title number x mc68hc681 user? manual motorola motorola mc68hc681 user? manual xiii list of tables table page number title number 2-1. signal summary ..............................................................................................2-1 4-1. register addressing and address-triggered commands ...............................4-3 4-2. programming of input port functions .............................................................4-3 4-3. programming of output port functions ...........................................................4-4 4-4. selection of clock sources for the counter/timer ..........................................4-5 4-5. baud-rate generator characteristics crystal or clock = 3.6864 mhz .........4-22 a-1. MC68HC2681 signal summary ..................................................................... a-3 a-2. MC68HC2681 register addressing and address-triggered commands ...... a-5 motorola mc68hc681 user? manual xi list of illustrations figure page number title number 1-1. 68hc681block diagram ...................................................................................1-2 4-1. programming block diagram ...........................................................................4-2 5-1. clock timing ....................................................................................................5-3 5-2. reset timing .................................................................................................5-4 5-3. read cycle bus timing ....................................................................................5-6 5-4. write cycle bus timing ....................................................................................5-6 5-5. interrupt cycle bus timing ...............................................................................5-7 5-6. port timing .......................................................................................................5-7 5-7. interrupt reset timing ......................................................................................5-8 5-8. transmitter timing ...........................................................................................5-8 5-9. receiver timing ...............................................................................................5-9 5-10. transmitter operation ....................................................................................5-10 5-11. receiver operation ........................................................................................5-11 5-12. wake-up mode operation .............................................................................5-12 a-1. MC68HC2681 block diagram ......................................................................... a-2 a-2. clock timing ................................................................................................... a-7 a-3. reset timing ................................................................................................ a-8 a-4. bus timing ...................................................................................................... a-8 a-5. port timing ...................................................................................................... a-9 a-6. interrupt reset timing .................................................................................... a-9 a-7. transmitter timing ........................................................................................ a-10 a-8. receiver timing ............................................................................................ a-10 a-9. transmitter operation ................................................................................... a-11 a-10. receiver operation ....................................................................................... a-12 a-11. wake-up mode operation ............................................................................ a-13 motorola mc68hc681 user? manual 1-1 1 section 1 introduction the mc68hc681 dual universal asynchronous receiver/transmitter (duart) is part of the m68000 family of peripherals and directly interfaces to the mc68000 processor via an asynchronous bus structure. the mc68hc681 consists of these major sections: internal control logic timing logic interrupt control logic bidirectional 8-bit data bus buffer two independent communication channels (a and b) 6-bit parallel input port 8-bit parallel output port the MC68HC2681 dual asynchronous receiver/transmitter (duart) is functionally equivalent to the mc68hc681 with some minor differences. the description of the mc68hc681 applies to the MC68HC2681 except for the areas described in appendix a MC68HC2681 located in the back of this document. figure 1-1 is a basic block diagram of the mc68hc681 and should be referred to during the discussion of its features, which include the following: m68000 bus compatible two independent full-duplex asynchronous receiver/transmitter channels maximum data transfer rate: 1x ?1 mbits/second 16x ?250 kbits/second quadruple-buffered receiver data registers double-buffered transmitter data registers independently programmable baud rate for each receiver and transmitter selectable from: 18 fixed rates: 50 to 38.4k baud one user defined rate derived from a programmable timer/counter external 1x clock or 16x clock introduction 1-2 mc68hc681 user? manual motorola 1 figure 1-1. mc68hc681 block diagram internal control logic channel a rs4-rs1 external interface txda rxda x1 x2 processor interface v cc irq dtack r/w cs internal data bus cra command register w mr1a mode register 1 r/w mr2a mode register 2 r/w sra status register r thra transmit holding reg w rhra receive holding reg (3) r rhra (2) tba rba transmit shift reg rhra (1) receive shift register channel b txdb rxdb crb command register w mr1b mode register 1 r/w mr2b mode register 2 r/w srb status register r thrb transmit holding reg w rhrb receive holding reg (3) r rhrb (2) tbb rbb transmit shift register rhrb (1) receive shift register input port ipcr input port change reg r aux control reg (4 bits) w acr input port (6 bits) r acr * same acr as in interrupt control logic * output port opcr output port config reg w output port reg (8 bits) w opr fifo timing logic current count in counter mode may be read * interrupt control logic imr interrupt mask reg w interrupt status reg r aux control reg (4 bits) w acr * same acr as in input port * d7-d0 data bus buffer csra channel a clock select reg w channel b clock select reg w acr auxiliary control reg (4 bits) w csrb counter/timer upper register (most signif 8 bits) w * counter/timer lower register (least signif 8 bits) w * isr gnd op7-op0 reset ip5-ip0 interrupt vector reg r/w ivr iack fifo introduction motorola mc68hc681 user? manual 1-3 1 programmable data format five to eight data bits odd, even, force parity, or no parity one, one and one-half, or two stop bits programmable channel modes normal (full duplex) automatic echo local loopback remote loopback automatic wake-up mode for multidrop applications multifunction 6-bit input port clock or control input functions change-of-state detection on four inputs multifunction 8-bit output port individual bit set/reset capability status/interrupt signal programmable outputs multifunction 16-bit programmable counter/timer versatile interrupt system single interrupt output with eight maskable interrupting conditions interrupt vector output on interrupt acknowledge programmable output port can be configured to provide as many as six separate wire-orable interrupt outputs parity, framing, and overrun error detection false-start bit detection line-break detection and generation break detection starting in the middle of a character start-end break interrupt/status on-chip crystal oscillator ttl compatible single +5v power supply introduction 1-4 mc68hc681 user? manual motorola 1 1.1 internal control logic the internal control logic receives operation commands from the central processing unit (cpu) and generates appropriate signals to the internal sections to control device operation. the internal control logic allows access to the registers within the duart and performs various commands by decoding the four register-select lines (rs1 through rs4). besides the four register-select lines, there are three other inputs to the internal control logic from the cpu: read/write (r/w ), which allows read and write transfers between the cpu and duart via the data bus buffer; chip-select (cs ), which is the duart chip-select; and reset (reset ), which initializes or resets the duart. the data transfer acknowledge (dtack ) signal, which is asserted during read, write, or interrupt-acknowledge cycles, is the internal control logic output. the dtack signal indicates to the cpu that data has been latched on a cpu write cycle or that valid data is present on the data bus during a cpu read cycle or interrupt-acknowledge (iack ) cycle. 1.2 timing logic the timing logic consists of a crystal oscillator, a baud-rate generator (brg), a programmable 16-bit counter/timer (c/t), and four clock selectors. the crystal oscillator operates directly from a 3.6864 mhz crystal connected across the x1 and x2 inputs or from an external clock of the appropriate frequency connected to x1. the x1 clock serves as the basic timing reference for the baud-rate generator, the c/t, and other internal circuits. the part can operate without an x1 clock but with the following restrictions: the x1 input must be connected to gnd or v cc the receiver(s) and transmitter(s), if used, must not be programmed to select any of the 18 standard rates generated by the brg the counter/timer, if used, must not be programmed to the x1 or x1/16 selection the change-detect on ip0-ip3 will not operate dtack will not be generated on any bus cycle the baud-rate generator operates from the x1 clock input and can generate 18 commonly used data communication baud rates ranging from 50 to 38.4k by producing internal clock outputs at 16 times the actual baud rate. the c/t can produce a 16x clock for other baud rates by counting down its programmed clock source. other baud rates can also be derived by connecting 16x or 1x clocks to certain input port pins that have alternate functions as receiver or transmitter clock inputs. four clock selectors allow the independent selection of any of these baud rates for each receiver and transmitter. customers can program the 16- bit c/t within the duart to use one of several clock sources as its input. the output of the c/t is available to the internal clock selectors and can also be programmed to appear at parallel output op3. in the timer mode, the c/t acts as a programmable divider and can generate a square-wave output at op3. in the counter mode, the c/t can be started and stopped under program control. when stopped, the cpu can read its contents. the counter counts down the number of pulses stored in the concatenation of the c/t upper register and c/t lower register and produces an interrupt. this is a system-oriented feature that can be used to record timeouts when implementing various application protocols. introduction motorola mc68hc681 user? manual 1-5 1 1.3 interrupt control logic the following registers are associated with the interrupt control logic: interrupt mask register (imr) interrupt status register (isr) auxiliary control register (acr) interrupt vector register (ivr) refer to section 4 programming and register descriptions for more complete information on these registers. a single active-low interrupt output (irq ) can notify the processor that any of eight internal events has occurred. these eight events are described in the discussion of the interrupt status register (isr) in section 4 programming and register descriptions . customers can program the interrupt mask register (imr) to allow only certain conditions to cause irq to be asserted while the cpu can read the isr to determine all currently active interrupting conditions. when an active-low interrupt acknowledge signal (iack ) from the processor is asserted while the duart has an interrupt pending, the duart will place the contents of the interrupt vector register (ivr) on the data bus and assert the data transfer acknowledge signal (dtack ). if the duart has no pending interrupt, it ignores iack cycles. in addition, customers can program the parallel outputs op3 through op7 to provide discrete interrupt outputs for the transmitters, the receivers, and the c/t. 1.4 data bus buffer the data bus buffer provides the interface between the external and internal data buses. it is controlled by the internal control logic to allow read and write data transfer operations to occur between the controlling cpu and duart by way of the eight parallel data lines (do through d7). 1.5 communication channels a and b each communication channel comprises a full-duplex asynchronous receiver/transmitter (uart). the operating frequency for each receiver and each transmitter can be selected independently from the baud-rate generator, the c/t, or from an external clock. the transmitter accepts parallel data from the cpu, converts it to a serial bit stream, inserts the appropriate start, stop, and optional parity bits, and outputs a composite serial stream of data on the txd output pin. the receiver accepts serial data on the rxd pin, converts this serial input to parallel format, checks for a start bit, stop bit, parity bit (if any), or break condition, and transfers an assembled character to the cpu during read operations. 1.6 input port the cpu reads the inputs to this 6-bit port (ip0 through ip5). high or low inputs to the input port result in the cpu reading a logic one or logic zero, respectively; that is, there is no inversion of the logic level. each input port bit also has an alternate control function capability. the alternate functions can be enabled/disabled on a bit-by-bit basis. introduction 1-6 mc68hc681 user? manual motorola 1 four change-of-state detectors are associated with inputs ip0, ip1, ip2, and ip3. if a high- to-low or low-to-high transition occurs on any of these inputs and the new level is stable for more than 25 to 50 microseconds (best-to-worst case times), the corresponding bit in the input port change register (ipcr) will be set. the sampling clock of the change detectors is the x1/96 tap of the baud-rate generator (the 2400 baud tap), which is 38.4khz if x1 is 3.6864mhz. a new input level must be sampled on two consecutive sample clocks to produce a change detect. also, customers can program the duart to allow a change of state to generate an interrupt to the cpu. the ipcr bits are cleared when the cpu reads the register. 1.7 output port this 8-bit multipurpose output port can be used as a general-purpose output port. associated with the output port is an output port register (opr). all bits of the opr can be individually set and reset. a bit is set by performing a write operation at the appropriate address with the accompanying data specifying the bits to be set (one equals set and zero equals no change). similarly, a bit is reset by performing a write operation at another address with the accompanying data specifying the bits to be reset (one equals reset and zero equals no change). the opr stores data that is to be output at the output port pins. unlike the input port, if a particular bit of the opr is set to a logic one or logic zero, the output pin will be at a low or high level, respectively. thus, a logic inversion occurs internal to the duart with respect to this register. the outputs are complements of the data contained in the opr. table 4-1 and section 4 programming and register descriptions provide more information on the address location of the output port register and setting and resetting bits of this register. besides general-purpose outputs, the outputs can be individually assigned specific auxiliary functions serving the communication channels. the assignment is accomplished by appropriately programming the channel a and b mode registers (mr1a, mr1b, mr2a, and mr2b) and the output port configuration register (opcr). section 4 programming and register descriptions provides more information on the mode registers and the opcr. motorola mc68hc681 user? manual 2-1 2 section 2 signal descriptions this section briefly describes the input and output signals. table 2-1 provides a quick reference for determining a signal? pin number, its use as an input or output, whether it is active high or low, and the section that contains more information about its operation. note the terms assertion and negation will be used extensively to avoid confusion when dealing with a mixture of "active low" and "active high" signals. the term assert or assertion indicates that a signal is active or true, independent of whether that level is represented by a high or low voltage. the term negate or negation indicates that a signal is inactive or false. table 2-1. signal summary signal name mnemonic pin no. in/out active state refer to para. no. p pkg. fn pkg. power supply (5 v) v cc 40 44 in high 2.1 ground gnd 20 22 in low 2.1 crystal input or external clock x1 32 36 in 2.2 crystal output x2 33 37 out 2.3 reset reset 34 38 in low 2.4 chip select cs 35 39 in low 2.5 read/write r/w 8 9 in high/low 2.6 data transfer acknowledge dtack 9 10 out 1 low 2.7 register-select bus bit 4 rs4 6 7 in high 2.8 register-select bus bit 3 rs3 5 6 in high 2.8 register-select bus bit 2 rs2 3 4 in high 2.8 register-select bus bit 1 rs1 1 2 in high 2.8 bidirectional-data bus bit 7 d7 19 21 in/out high 2.9 bidirectional-data bus bit 6 d6 22 25 in/out high 2.9 bidirectional-data bus bit 5 d5 18 20 in/out high 2.9 bidirectional-data bus bit 4 d4 23 26 in/out high 2.9 bidirectional-data bus bit 3 d3 17 19 in/out high 2.9 signal descriptions 2-2 mc68hc681 user? manual motorola 2 2.1 v cc and gnd power is supplied to the duart using these two signals. v cc is power ( + 5 volts) and gnd is the ground connection. 2.2 crystal input or external clock (x1) this input is one of two connections to a crystal or a connection to an external cmos-level clock. if a crystal is used, a capacitor of approximately 10 to 15 picofarads should be connected from this pin to ground. bidirectional-data bus bit 2 d2 24 27 in/out high 2.9 bidirectional-data bus bit 1 d1 16 18 in/out high 2.9 bidirectional-data bus bit 0 (least-significant bit) d0 25 28 in/out high 2.9 interrupt request irq 21 24 out 1 low 2.10 interrupt acknowledge iack 37 41 in low 2.11 channel a transmitter serial data txda 30 33 out 2.12 channel a receiver serial data rxda 31 35 in 2.13 channel b transmitter serial data txdb 11 13 out 2.14 channel b receiver serial data rxdb 10 11 in 2.15 parallel input 5 ip5 38 42 in 2.16.1 parallel input 4 ip4 39 43 in 2.16.2 parallel input 3 ip3 2 3 in 2.16.3 parallel input 2 ip2 36 40 in 2.16.4 parallel input 1 ip1 4 5 in 2.16.5 parallel input 0 ip0 7 8 in 2.16.6 parallel output 7 op7 15 17 out 2 2.17.1 parallel output 6 op6 26 29 out 2 2.17.2 parallel output 5 op5 14 16 out 2 2.17.3 parallel output 4 op4 27 30 out 2 2.17.4 parallel output 3 op3 13 15 out 2 2.17.5 parallel output 2 op2 28 31 out 2.17.6 parallel output 1 op1 12 14 out 2.17.7 parallel output 0 op0 29 32 out 2.17.8 notes: 1. requires a pullup resistor 2. may require a pullup resistor, depending on its programmed function. table 2-1. signal summary (continued) signal name mnemonic pin no. in/out active state refer to para. no. p pkg. fn pkg. signal descriptions motorola mc68hc681 user? manual 2-3 2 2.3 crystal input (x2) this input is an additional connection to a crystal (see section 2 signal descriptions). if an external cmos-level clock is used, this pin must be left open. if a crystal is used, a capacitor of approximately 10 to 15 picofarads should be connected from this pin to ground. 2.4 reset (reset ) the duart can be reset by asserting the reset signal or by programming the appropriate command register. a hardware reset (assertion of reset ) clears the following registers: status registers a and b (sra and srb) interrupt mask register (imr) interrupt status register (isr) output port register (opr) output port configuration register (opcr) reset performs the following operations: initializes the interrupt vector register (ivr) to 0f 16 places parallel outputs op0 through op7 in the high state places the counter/timer in timer mode places channels a and b in the inactive state with the transmitter serial-data outputs (txda and txdb) in the mark (high) state. software resets are not as encompassing and are achieved by appropriately programming the channel a and/or b command registers. reset commands can be programmed through the command register to reset the receiver, transmitter, error status, or break-change interrupts for each channel. refer to section 4 programming and register descriptions for more information. 2.5 chip-select (cs ) this active-low input signal, when low, enables data transfers between the cpu and duart on the data lines (d0 through d7). these data transfers are controlled by read/write (r/w ) and the register-select inputs (rs1 through rs4). when chip-select is high, the d0 through d7 data lines are placed in the high-impedance state. 2.6 read/write (r/w ) when high, this input indicates a read cycle; when low, it indicates a write cycle. assertion of the chip-select input initiates a cycle. signal descriptions 2-4 mc68hc681 user? manual motorola 2 2.7 data transfer ackowledge (dtack ) this three-state active low output is asserted in read, write, or interrupt-acknowledge (iack ) cycles to indicate the proper transfer of data between the cpu and duart. if there is no pending interrupt on an iack cycle, dtack is not asserted. dtack is an ?ctive rescind? signal: at the end of a transfer, it drives high momentarily, then is three-stated so that it can be wire-anded with other dtack sources, like an open-drain signal. 2.8 register-select bus (rs1?s4) the register-select bus lines during read/write operations select the duart internal registers, ports, or commands. 2.9 data bus (d0?7) these bidirectional three-state data lines transfer commands, data, and status between the cpu and duart. d0 is the least-significant bit. 2.10 interupt request (irq ) this active-low, open-drain output signals the cpu that one or more of the eight maskable interrupting conditions are true. 2.11 interupt ackowledge (iack ) this active-low input indicates an interrupt-acknowledge cycle. if there is an interrupt pending (irq asserted) and this pin is asserted, the duart responds by placing the interrupt vector on the data bus and then asserting dtack . if there is no interrupt pending (irq negated), the duart ignores this pin. 2.12 channel a/b transmitter serial-data output (txda/txdb) the independent transmitter serial-data outputs for channel a and b transmit the least-significant bit first. the output is held high (mark condition) when its associated transmitter is disabled, idle, or operating in the local loopback mode. (mark is high and space is low.) data is shifted out from this pin on the falling edge of the programmed clock source. 2.13 channel a/b receiver serial-data input (rxda/rxdb) the independent receiver serial-data inputs for channel a and b receive the least-significant bit first. data on these pins is sampled on the rising edge of the programmed clock source. 2.14 parallel inputs (ip0?p5) the parallel inputs can be used as general-purpose inputs. however, each pin also has an alternate function(s) described below. 2.14.1 ip0 this input can be used as the channel a clear-to-send active-low input (ctsa ). a change-of- state detector is also associated with this input. signal descriptions motorola mc68hc681 user? manual 2-5 2 2.14.2 ip1 this input can be used as the channel b clear-to-send active-low input (ctsb ). a change-of- state detector is also associated with this input. 2.14.3 ip2 this input can be used as the channel b receiver external clock input (rxcb), or the counter/timer external clock input. when this input functions as the external clock to the receiver, the received data is sampled on the rising edge of the clock. a change-of-state detector is also associated with this input. 2.14.4 ip3 this input can serve as the channel a transmitter external clock input (txca). when this input functions as the external clock to the transmitter, the transmitted data is clocked on the falling edge of the clock. a change-of-state detector is also associated with this input. 2.14.5 ip4 this input can be used as the channel a receiver external clock input (rxca). when this input functions as the external clock to the receiver, the received data is sampled on the rising edge of the clock. 2.14.6 ip5 this input can serve as the channel b transmitter external clock (txcb). when this input is used as the external clock to the transmitter, the transmitted data is clocked on the falling edge of the clock. 2.15 parallel outputs (op0?p7) the parallel outputs can be used as general-purpose outputs; however, each pin also has an alternate function(s), described below. 2.15.1 op0 this output can function as the channel a transmitter active-low request-to-send (rtsa ) output, or as the channel a receiver active-low ready-to-receive (rtra ) output. when used for rtsa , it is automatically negated by the transmitter. when used for rtra , the receiver automatically negates and reasserts op0. 2.15.2 op1 this output can serve as the channel b transmitter active-low request-to-send (rtsb ) output, or as the channel b receiver active-low ready-to-receive (rtrb ) output. when used for rtsb , the transmitter automatically negates op1 by the transmitter. when used for rtrb , the receiver automatically negates and reasserts op1. signal descriptions 2-6 mc68hc681 user? manual motorola 2 2.15.3 op2 this output can be used as the channel a transmitter 1x-clock or 16x-clock output or the channel a receiver 1x-clock output. 2.15.4 op3 this output can function as the open-drain active-low counter-ready output, the open-drain timer output, the channel b transmitter 1x-clock output, or the channel b receiver 1x-clock output. 2.15.5 op4 this output can serve as the channel a open-drain active-low receiver-ready or buffer-full interrupt outputs (rxrdya /ffulla ) by appropriately programming bit 6 of mode register 1a. 2.15.6 op5 this output can be used as the channel b open-drain active-low receiver-ready or buffer-full interrupt outputs (rxrdyb /ffullb ) by appropriately programming bit 6 of mode register 1b. 2.15.7 op6 this output can function as the channel a open-drain active-low transmitter-ready interrupt output (txrdya ). 2.15.8 op7 this output can serve as the channel b open-drain active-low transmitter-ready interrupt output (txrdyb ). motorola mc68hc681 user? manual 3-1 3 section 3 operation 3.1 transmitter the channel a and b transmitters are enabled for data transmission through their respective command registers (refer to section 4 programming and register descriptions ). the duart signals the cpu it is ready to accept a character by setting the transmitter-ready bit in the channel? status register. customers can program this condition to generate an interrupt request on the irq output, an interrupt request for channel a? transmitter on parallel output op6, or for channel b? transmitter on parallel output op7. when a character is loaded into the transmit buffer (tb), the above conditions for the respective channel are negated. data is transferred from the transmit holding register to the transmit shift register when the shift register is idle or has completed transmission of the previous character. the transmitter ready conditions are then re-asserted, providing one full character time of buffering. characters cannot be loaded into the transmit buffer while the transmitter is disabled. the transmitter converts the parallel data from the cpu to a serial bit stream on the transmitter serial-data output pin. it automatically sends a start bit followed by the programmed number of data bits, an optional parity bit, and the programmed number of stop bits. the least-significant bit is sent first. data is shifted out the transmit serial data output pin on the failing edge of the programmed clock source. after the transmission of the stop bits, if a new character is not available in the transmit holding register the transmitter serial-data output remains high and the transmitter-empty bit in the status register (sra and srb) will be set to a one. transmission resumes and the transmitter-empty bit is cleared when the cpu loads a new character into the transmit buffer (tba or tbb). if the transmitter receives a disable command, it will continue operating until the character in the transmit shift register is completely sent out. another character in the holding register is not sent but is not discarded; it will be sent when the transmitter is re-enabled. the transmitter can be reset through a software command (refer to section 2.4 reset ). if it is reset, operation ceases immediately and must be enabled through the command register before resuming operation. reset also discards any character in the holding register. if clear-to-send (cts ) operation is enabled, the cts input (alternate function of ip0 or ip1) must be low in order for the character to be transmitted. if it goes high in the middle of a transmission, the character in the shift register is transmitted and txd then remains in the marking state until cts again goes low. the transmitter can also be forced to send a continuous low condition by issuing a send-break command. the state of cts is ignored by the transmitter when it is to send a break. operation 3-2 mc68hc681 user? manual motorola 3 a send-break is deferred as long as the transmitter has characters to send, but if normal character transmission is inhibited by cts , the send-break will proceed. the send-break must be terminated by a stop-break, disable, or reset before normal character transmission can resume. customers can program the transmitter to automatically negate the request-to-send (rts) output (alternate function of op0 and op1) on completion of a message transmission. if the transmitter is programmed to operate in this manner, the rts output must be manually asserted before each message is transmitted. if op0 (or op1) is programmed in automatic rts mode, the rts output will be automatically negated when the transmitter is disabled and the transmit-shift register and holding register are both empty. in automatic rts mode, a character in the holding register is not held back by a disable, but no more characters can be written to the holding register after the transmitter is disabled. 3.2 receiver the channel a and b receivers are enabled for data reception through the respective channel? command register. the channel? receiver looks for the high-to-low (mark-to- space) transition of a start bit on the receiver serial-data input pin. if operating in 16x clock mode, the serial input data is re-sampled on the next 7 clocks. if the receiver serial data is sampled high, the start bit is invalid and the search for a valid start bit begins again. if receiver serial data is still low, a valid start bit is assumed and the receiver continues to sample the input at one bit time intervals (at the theoretical center of the bit) until the proper number of data bits and the parity bit (if any) have been assembled and one stop bit has been detected. data on the receiver serial data input pin is sampled on the rising edge of the programmed clock source. during this process, the least-significant bit is received first. the data is then transferred to a receive holding register (rhr) and the receiver-ready bit in the status register (sra or srb) is set to a one (see figure 3-1). this condition can be programmed to generate an interrupt request on the irq output, an interrupt request for channel a? receiver on parallel output op4, or an interrupt request for channel b? receiver on parallel output op5. if the character length is less than eight bits, the most significant unused bits in the receive holding register (rhr) are set to zero. if the stop bit is sampled as a 1, the receiver will immediately look for the next start bit. however, if the stop bit is sampled as a 0, either a framing error or a received break has occurred. if the stop bit is 0 and the data and parity (if any) are not all zero, it is a framing error; the damaged character is transferred to a holding register with the framing error flag set. if the receiver serial data remains low for one-half of the bit period after the stop bit was sampled, the receiver operates as if a new start bit transition has been detected. if the stop bit is 0 and the data and parity (if any) are also all zero, it is a break. a character consisting of all zeros will be loaded into a receive holding register (rhr) with the received-break bit (but not the framing error bit) set to a one. the receiver serial-data input must return to a high condition for at least one-half bit time before a search for the next start bit begins. operation motorola mc68hc681 user? manual 3-3 3 the receiver can detect a break that starts in the middle of a character provided the break persists completely through the next character time or longer. when the break begins in the middle of a character, the receiver will place the damaged character in a holding register with the framing error bit set. then, provided the break persists through the next character time, the receiver will also place an all-zero character in the next holding register with the received-break bit set. the parity error, framing error, overrun error, and received-break conditions (if any) set error and break flags in the status register at the received character boundary and are valid only when the receiver-ready bit (rxrdy) in the status register is set. a first-in first-out (fifo) stack is used in each channel? receive buffer logic and consists of three receive holding registers. the receiver buffer (rba or rbb) is composed of the fifo and a receive shift register connected to the receiver serial-data input. data is assembled in the shift register and loaded into the top-most empty fifo receive holding register position. thus, data flowing from the receiver to the cpu is quadruply buffered. the receiver-ready bit in the status register (sra or srb) is set whenever one or more characters are available to be read. a read of the receiver buffer produces an output of data from the top of the fifo stack. after the read cycle, the data at the top of the fifo stack and its associated status bits are "popped" and new data can be added at the bottom of the stack by the receive shift register. the fifo-full status bit is set if all three stack positions are filled with data. either the receiver-ready or the fifo-full status bits can be selected to cause an interrupt. in addition to the data byte, three status bits (parity error, framing error, and received break) are appended to each data character in the fifo (overrun is not). by programming the error-mode control bit in the channel? mode register, status can be provided for "character" or "block" modes. in the "character" mode, the status register (sra or srb) is updated on a character-by- character basis and applies only to the character at the top of the fifo. thus, the status must be read before the character is read. reading the character pops it and its error flags off the fifo. in the "block" mode, the status provided in the status register for the parity error, framing error, and received-break conditions is the logical or of these respective bits for all characters coming to the top of the fifo stack since the last reset error command was issued. that is, beginning at the last reset-error command issued, a continuous logical-or function of corresponding status bits is produced in the status register as each character comes to the top of the fifo stack. the block mode is useful in applications requiring the exchange of blocks of information where the software overhead of checking each character? error flags cannot be tolerated. in this mode, entire messages can be received and only one data integrity check is performed at the end of each message. although data reception in this manner has speed advantages, there are also disadvantages. because each character is not individually checked for error conditions by the software, if an error occurs within a message the error will not be recognized until the final check is performed. also, there is no indication of which character(s) is in error within the message. operation 3-4 mc68hc681 user? manual motorola 3 the block mode can only be used if either (or both) of two conditions can be guaranteed: 1. the length of the block is known before the last character of the block is read, so that the block error status can be read and cleared before reading the last character; 2. there will never be another character already present in the fifo until the last char- acter of the message is read (leaving the fifo empty), the status is read, and a reset error command is issued. otherwise, errors in the first character of the next block could be reported erroneously on the current block, or they could be prematurely cleared and not reported in the error status of the next block. in either mode, reading the status register (sr) does not affect the fifo. the fifo is "popped" only when the receive buffer (rba or rbb) is read. if all three of the fifo? receive holding registers are full when a new character is received, that character is held in the receive shift register until a fifo position is available. if an additional character is received while this state exists, the contents of the fifo are not affected, but the character previously in the shift register is lost and the overrun-error status bit will be set upon receipt of the start bit of the new overrunning character. to support flow control, a receiver can automatically negate and reassert the ready-to- receive (rt r ) output (alternate function of parallel outputs op0 and op1). the rts and rtr functions both use op0 (channel a) and/or op1 (channel b). both functions should not be enabled for the same channel at the same time. if programmed to operate in this mode, the ready-to-receive output will automatically be negated by the receiver when a valid start bit is received and the fifo stack is full. when a fifo position becomes available, the ready-to-receive output will be reasserted automatically by the receiver. connecting the ready-to-receive output to the clear-to-send (cts ) input of a transmitting device, prevents overrun errors in the receiver. the rt r output must be manually asserted the first time. thereafter, the receiver will control the rt r output. if the fifo stack contains characters and the receiver is then disabled, the characters in the stack can still be read but no additional characters can be received until the receiver is again enabled. if the receiver is disabled while receiving a character, or while there is a character in the shift register waiting for a fifo opening, these characters are lost. if the receiver is reset, the fifo stack and all of the receiver status bits, the corresponding output ports, and the interrupt request are reset. no additional characters can be received until the receiver is again enabled. 3.3 looping modes besides the normal operation mode in which the receiver and transmitter operate independently, each duart channel can be configured to operate in various looping modes that are useful for local and remote system diagnostic functions. these modes are described in the following paragraphs with additional information available in section 4 programming and register descriptions . operation motorola mc68hc681 user? manual 3-5 3 3.3.1 automatic-echo mode in this mode, the channel automatically retransmits the received data on a bit-by-bit basis. the local cpu-to-receiver communication continues normally but the cpu-to-transmitter link is disabled. 3.3.2 local-loopback mode in this mode, the transmitter output is internally connected to the receiver input. the external txd pin is held in the mark (high) state in this mode. this mode is useful for testing the operation of a local duart channel. by sending data to the transmitter and checking that the data assembled by the receiver is the same data that was sent, proper channel operation can be assured. in this mode the cpu-to-transmitter and cpu-to-receiver communications continue normally. 3.3.3 remote-loopback mode in this mode, the channel automatically retransmits the received data on a bit-by-bit basis. the local cpu-to-receiver and cpu-to-transmitter links are disabled. this mode is useful in testing the receiver and transmitter operation of a remote channel. this mode requires the remote channel receiver to be enabled. 3.4 multidrop mode customers can program the channel to operate in a wake-up mode for multidrop applications. this mode is selected by setting bits three and four in mode register one (mr1). in this mode of operation, a master station? channel, connected to several slave stations (a maximum of 256 unique slave stations), transmits an address character followed by a block of data characters targeted for one or more of the slave stations. in this mode, the channel receivers within the slave stations are disabled, but they continuously monitor the data stream sent out from the master station. when the slave station? channel receivers detect any address character in the data stream, each receiver notifies its respective cpu by setting receiver ready (rxrdy) and generating an interrupt, if programmed to do so. each slave station cpu then compares the received address to its station address and enables its receiver if it wants to receive the subsequent data from the master station. slave stations that are not addressed continue monitoring the data stream for the next address character. an address character flags the end of one block of data and the start of another. after receiving a block of data, the slave station? cpu may disable the channel receiver and re-initiate the process. a transmitted character from the master station consists of a start bit, the programmed number of data bits, an address/data (a/d) bit flag, and the programmed number of stop bits. the address/data bit identifies to the slave station? channel whether the character should be interpreted as an address character or a data character. the character is interpreted as an address character if the a/d bit is set to a one or interpreted as a data character if it is set to a zero. the polarity of the transmitted address/data bit is selected by programming bit two in mode register one (mr1) to a one for an address character and to a zero for data characters. customers should program the mode register prior to loading the corresponding data or address characters into the transmit buffer (tba or tbb). operation 3-6 mc68hc681 user? manual motorola 3 in the multidrop mode, the receiver continuously monitors the received data stream regardless of whether it is enabled or disabled. if the receiver is disabled, it sets the receiver ready status bit and loads the character into the fifo receive holding register stack provided the received address/data bit is a one (address tag). the received character is discarded if the received address/data bit is a zero (data tag). if the receiver is enabled, all received characters are transferred to the cpu by way of the receive holding register stack during read operations. in either case, the data bits are loaded into the data portion of the fifo stack while the address/data bit is loaded into the status portion of the fifo stack normally used for parity error (status register bit five). framing error, overrun error, and break- detection operate normally regardless of whether the receiver is enabled or disabled. the address/data bit takes the place of the parity bit and parity is neither calculated nor checked for characters in this mode. nevertheless, messages in this mode can still contain error detection and correction information. one way to provide error detection (if 8-bit characters are not required) would be to use software to calculate parity and append it to 5-, 6-, or 7-bit characters. another way to provide error detection for the entire message would be to use cyclic redundancy checks, or hamming codes similar to those used in synchronous protocols, perform the check in software, and append the check character(s) to the end of the message. 3.5 counter/timer the 16-bit counter/timer (c/t) can operate in a counter mode or a timer mode. in either mode, customers can program the c/t input (clock source) to come from several sources and program the c/t output to appear on output port pin op3. the value (preload value) stored in the concatenation of the c/t upper register (ctur) and the c/t lower register (ctlr) can be from 0001 16 through ffff 16 and can be changed at any time. in counter mode, the cpu can start and stop the c/t. this mode allows the c/t to function as a system stopwatch, a real-time single interrupt generator, or a device watchdog. in timer mode, the c/t runs continuously; the cpu cannot start or stop it. instead, the cpu only resets the c/t interrupt. this mode allows the c/t to be used as a programmable clock source for channels a and b, or periodic interrupt generator. at power-up and after reset, the c/t operates in timer mode. 3.5.1 counter mode in counter mode, the c/t counts down from the preload value using the programmed counter clock source. the counter clock source can be the channel a transmitter clock, the channel b transmitter clock, the external clock on the x1 pin divided by sixteen, or an external clock on the input port pin ip2. the cpu can start and stop the counter, and can read the count value (cur:clr) if the counter is stopped. when a read at the start counter command address is performed, the counter is initialized to the preload value and begins a countdown sequence. when the counter counts from 0001 16 to 0000 16 (terminal count), the c/t-ready bit in the interrupt status register (isr[3]) is set. operation motorola mc68hc681 user? manual 3-7 3 customers can program the counter to generate an interrupt request for this condition on the irq output or output pin op3. after 0000 16 the counter counts to ffff 16 , and continues counting down from there. if the cpu changes the preload value, the counter will not recognize the new value until it receives the next start counter command (and is reinitialized). when a read at the stop counter command address is performed, the counter stops the countdown sequence and clears isr[3]. the count value should only be read while the counter is stopped because only one of the count registers (either cur or clr) can be read at a time. if the counter is running, a decrement of clr that requires a borrow from the cur could take place between the two reads. 3.5.2 timer mode in timer mode, the c/t generates a square-wave output derived from the programmed timer input (clock source). the timer clock source can be the external clock on the x1 input pin divided by one or sixteen, or it can be an external input on input port pin ip2 divided by one or sixteen. the square wave generated by the timer has a period of 2x (preload value) x (period of clock source), is available as a clock source for both communications channels and can be programmed to appear on output pin op3. the timer runs continuously; the cpu cannot stop it. because the timer cannot be stopped, the count value (cur:clr) should not be read. when a read at the start counter command address is performed, the timer terminates the current countdown sequence, sets its output to 1 (appears uninverted at op3), is initialized to the preload value, and begins a new countdown sequence. when the counter counts from 0001 16 (terminal count), it inverts its output, is re-initialized to the preload value and repeats the countdown sequence. after reaching terminal count a second time, the timer sets the c/t-ready bit in the interrupt status register (isr[3]), inverts its output, is re-initialized again, and begins a new countdown sequence. customers can program the timer to generate an interrupt request for this condition (every second countdown cycle) on the irq output. if the cpu changes the preload value, the timer will not recognize the new value until either (a) it reaches the next terminal count and is reinitialized automatically, or (b) it is forced to re-initialize by a start command. when a read at the stop counter command address is performed, the timer clears isr[3] but does not stop. because in timer mode the c/t runs continuously, it should be completely configured (preload value loaded and start counter command issued) before programming the timer output to appear on op3. motorola mc68hc681 user? manual 4-1 4 section 4 programming and register descriptions 4.1 programming descriptions customers program the duart by writing control words into the appropriate registers. the status registers provide operational feedback that the cpu reads. table 4-1 describes the duart register address and address-triggered commands. figure 4-1 illustrates a block diagram of the duart from a programming perspective and details the register configuration for each block. table 4-1 and figure 4-1 should be referred to during the discussion of the programming features of the duart. programming and register descriptions 4-2 mc68hc681 user? manual motorola 4 figure 4-1. programming block diagram internal control logic channel a rs4-rs1 external interface txda rxda x1 x2 processor interface v cc irq dtack r/w cs internal data bus cra command register w mr1a mode register 1 r/w mr2a mode register 2 r/w sra status register r thra transmit holding reg w rhra receive holding reg (3) r rhra (2) tba rba transmit shift reg rhra (1) receive shift register channel b txdb rxdb crb command register w mr1b mode register 1 r/w mr2b mode register 2 r/w srb status register r thrb transmit holding reg w rhrb receive holding reg (3) r rhrb (2) tbb rbb transmit shift register rhrb (1) receive shift register input port ipcr input port change reg r aux control reg (4 bits) w acr input port (6 bits) r acr * same acr as in interrupt control logic * output port opcr output port config reg w output port reg (8 bits) w opr fifo timing logic current count in counter mode may be read * interrupt control logic imr interrupt mask reg w interrupt status reg r aux control reg (4 bits) w acr * same acr as in input port * d7-d0 data bus buffer csra channel a clock select reg w channel b clock select reg w acr auxiliary control reg (4 bits) w csrb counter/timer upper register (most signif 8 bits) w * counter/timer lower register (least signif 8 bits) w * isr gnd op7-op0 reset ip5-ip0 interrupt vector reg r/w ivr iack fifo programming and register descriptions motorola mc68hc681 user? manual 4-3 4 table 4-2 summarizes the various input port pin functions. table 4-1. register addressing and address-triggered commands rs4 rs3 rs2 rs1 read (r/w = 1) write (r/w = 0) 0000 mode register a (mr1a, mr2a) mode register a (mr1a, mr2a) 0001 status register a (sra) clock-select register a (csra) 0010 clock-select register a 1 (csra) command register a (cra) 0011 receiver buffer a (rba) transmitter buffer a (tba) 0100 input port change register (ipcr) auxiliary control register (acr) 0101 interrupt status register (isr) interrupt mask register (imr) 0110 counter mode: current msb of counter (cur) counter/timer upper register (ctur) 0111 counter mode: current lsb of counter (clr) counter/ timer lower register (ctlr) 1000 mode register b (mr1b, mr2b) mode register b (mr1b, mr2b) 1001 status register b (srb) clock-select register b (csrb) 1010 clock-select register b 2 (csrb) command register b (crb) 1011 receiver buffer b (rbb) transmitter buffer b (tbb) 1100 interrupt-vector register (ivr) interrupt-vector register (ivr) 1101 input port (ip) output port configuration register (opcr) 1110 start-counter command 3 output port register (opr) bit set command 3 1111 stop-counter command 3 bit reset command 3 notes: 1. reading from this address is prohibited in the mc68681. 2. address triggered commands. table 4-2. programming of input port functions function input port pin ip5 ip4 ip3 ip2 ip1 ip0 general purpose default* default* default* default* default* default* change-of-state detector no no yes yes yes yes external counter 1x clock input acr[6:4] = 000 external timer 16x clock input acr[6:4] = 100 external timer 1x clock input acr[6:4] = 101 programming and register descriptions 4-4 mc68hc681 user? manual motorola 4 table 4-3 summarizes the various output port pin functions. rxca 16x csra[7:4] = 1110 rxca 1x csra[7:4] = 1111 txca 16x csra[3:0] = 1110 txca 1x csra[3:0] = 1111 rxcb 16x csrb[7:4] = 1110 rxcb 1x csrb[7:4] = 1111 txcb 16x csab[3:0] = 1110 txcb 1x csrb[3:0] = 1111 txctsa mr2a[4] = 1 txctsb mr2b[4] = 1 note: the pin is in this mode unless program med to operate in another mode. table 4-3. programming of output port functions function output port pin op7 op6 op5 op4 op3 op2 op1 op0 general purpose opcr[7] = 0 opcr[6] = 0 61pcr[5] = 0 opcr[4] = 0 opcr[3:2] = 00 opcr[1:0] = 00 mr1b[7] = 0 mr2b[5] = 0 mr1b[7] = 0 mr2a[5] = 0 ctrdy opcr[3:2] = 01, acr[6] = 0* timer output opcr[3:2] = 01, acr[6] = 1* txcb 1x opcr[3:2] = 10 rxcb opcr[3:2] = 11 txca 16x opcr[1:0] = 01 txca 1x opcr[1:0] = 10 rxca 1x opcr[1:0] = 11 table 4-2. programming of input port functions (continued) function input port pin ip5 ip4 ip3 ip2 ip1 ip0 programming and register descriptions motorola mc68hc681 user? manual 4-5 4 table 4-4 summarizes the various clock sources that can be selected for the counter/ timer. customers should use caution if the contents of a register are changed during receiver/ transmitter operation as certain changes can produce undesired results. for example, changing the number of bits per character while the transmitter is active can transmit an incorrect character. the contents of the clock-select register (csr) and bit 7 of the auxiliary control register (acr[7]) should only be changed after the receiver(s) and transmitter(s) have been issued software rx and tx reset commands. most bits of the mode registers should not be changed during receiver/transmitter operation, except that in multidrop parity mode, the address/data parity type bit can be changed at any time. txrdya opcr[6] = 1* txrdyb opcr[7] = 1* rxrdya opcr[4] = 1 mr1a[6] = 0* rxrdyb opcr[5] = 1 mr1b[6] = 0* ffulla opcr[4] = 1, mr1a[6] = 1* ffullb opcr[5] = 1 mr1b[6] = 1* rxrtra mr1a[7] = 1 txrtsa mr2a[5] = 1 rxrtrb mr1b[7] = 1 txrtsb mr2b[5] = 1 note: the pin requires a pull-up resistor. table 4-4. selection of clock sources for the counter/timer acr[6] = 0 (counter mode) acr[6] = 1 (timer mode) counter mode clock sources acr[5:4] = timer mode clock sources acr[5:4] = input port pin ip2 00 input port pin ip2 00 channel a 1x transmitter clock txca 01 input port pin ip2 divided by 16 01 channel b 1x transmitter clock txcb 10 crystal/clock x1 10 crystal/clock x1 divided by 16 11 crystal/clock x1 divided by 16 11 table 4-3. programming of output port functions (continued) function output port pin op7 op6 op5 op4 op3 op2 op1 op0 programming and register descriptions 4-6 mc68hc681 user? manual motorola 4 similarly, certain changes to the auxiliary control register (acr bits six through four) should only be made while the counter/timer (c/t) is not used (i.e., stopped if in counter mode, output and/or interrupt masked in timer mode). channel a mode registers mr1a and mr2a are accessed via an auxiliary pointer. the pointer is set to mode register one (mr1a) by reset or by issuing a "reset pointer" command via the channel a command register. any read or write of the mode register switches the pointer to mode register two (mr2a). all subsequent accesses will address mr2a unless the pointer is reset to mr1a as described above. the channel b mode registers mr1b and mr2b are accessed by an identical pointer independent of the channel a pointer. mode, command, clock-select, and status registers are duplicated for each channel to allow independent operation and control (except that both channels are restricted to baud rates that are in the same set). 4.2 register bit formats rx rtr?ontrol 0 = disabled 1 = enabled rx irq = select 0 = rxrdy 1 = ffull error mode 0 = character 1 = block parity mode (bits 4 and 3) 0 0 = with parity 0 1 = force parity 1 0 = no parity 1 1 = multidrop mode parity type with parity 0 = even 1 = odd channel a/b mode register 1 (mr1a/mr1b) 7 654321 0 rx rtr rx irq error mode parity mode parity type bits per character programming and register descriptions motorola mc68hc681 user? manual 4-7 4 force parity 0 = low 1 = high multidrop mode 0 = data 1 = address bits-per-character (bits 1 and 0) 0 0 = 5 0 1 = 6 1 0 = 7 1 1 = 8 channel mode (bits 7 and 6) 0 0 = normal 0 1 = automatic echo 1 0 = local loopback 1 1 = remote loopback tx rts?ontrol 0 = disabled 1 = enabled cts?nable transmitter 0 = disabled 1 = enabled stop bit length (bits 3, 2) 0 0 = 1 stop bit 0 1 = 1 stop bit 1 0 = 1.5 stop bits (async mode); 2 stop bits (sync mode) 1 1 = 2 stop bits channel a mode register 2 (mr2a/mr2b) 76543210 channel mode tx rts cts stop bit length unused clock-select register a/b (csra/csrb) 76543210 receiver-clock select transmitter clock select programming and register descriptions 4-8 mc68hc681 user? manual motorola 4 receiver (bits 7-4) and transmitter (bits 3-0) clock selec t all clock selects are 16x (async) except code 1111. ch a tx uses ip3 ch a rx uses ip4 ch b tx uses ip5 ch b rx uses ip2 bit 7 bit 6 bit 5 bit 4 set 1 set 2 0000 50 75 0001 110 110 0010 134.5 134.5 0011 200 150 0100 300 300 0101 600 600 0110 1200 1200 0111 1050 2000 1000 2400 2400 1001 4800 4800 1010 7200 1800 1011 9600 9600 1100 38.4k 19.2k 1101 timer timer 1110 ipn-16x ipn-16x 1111 ipn-1x ipn-1x channel a/b command register (cra/crb) 76543210 x miscellaneous commands transmitter commands receiver commands programming and register descriptions motorola mc68hc681 user? manual 4-9 4 x?ot used, may be set to either 0 or 1 miscellaneous commands (bits 6, 5, 4) 0 0 0 = no command 0 0 1 = reset mr pointer to mr1 0 1 0 = reset receiver 0 1 1 = reset transmitter 1 0 0 = reset error status 1 0 1 = reset channel? break-change interrupt 1 1 0 = start break 1 1 1 = stop break transmitter commands (bits 3 and 2) 0 0 = no action, stays in present mode 0 1 = transmitter enabled 1 0 = transmitter disabled 1 1 = don? use, indeterminate receiver commands (bits 1 and 0) 0 0 = no action, stays in present mode 0 1 = receiver enabled 1 0 = receiver disabled 1 1 = don? use, indeterminate these status bits are appended to the corresponding data character in the receive fifo and are valid only when the rxrdy bit is set. a read of the status register provides these bits (seven through five) from the top of the fifo together with bits four through zero. these bits are cleared by a reset error status command. in character mode, they are discarded when the corresponding data character is read from the fifo. all bits 0 = no 1 = yes channel a/b status register (sra/srb) 7*6*5*43210 received break framing error parity error overrun error txemt txrdy ffull rxrdy output port configuration register (opcr) 76543210 op7 op6 op5 op4 op3 op2 programming and register descriptions 4-10 mc68hc681 user? manual motorola 4 op7 0 = opr bit 7 1 = txrdyb op6 0 = opr bit 6 1 = txrdya op5 0 = opr bit 5 1 = rxrdyb/ffullb op4 0 = opr bit 4 1 = rxrdya/ffulla op3 (bits 3 and 2) 0 0 = opr bit 2 0 1 = c/t output 1 1 0 = txcb (1x) 1 1 = txcb (1x) op2 (bits 1 and 0) 0 0 = opr bit 2 0 1 = txca (16x) 1 0 = txca (1x) 1 1 = rxca (1x) alternate functions of op1 and op0 (txrts, rxrtr) are controlled by the mode registers, not the opcr. mr1a[7] and mr2a[5] control op0; mr1b[7] and mr2b[5] control op1. all bits, unless programmed for alternate function 0 = pin driven high 1 = pin driven low 1. if op3 is to be used for the timer output, customers should program the counter/timer for timer mode (acr[6] = 1), initialize the counter/timer preload registers (ctur and ctlr), and the start counter command issued before setting opcr[3:2] = 01. output port register (opr) 76543210 opr7 opr6 opr5 opr4 opr3 opr2 opr1 opr0 programming and register descriptions motorola mc68hc681 user? manual 4-11 4 brg set select. should only be changed after both channels have been reset and are disabled. 0 = set 1 1 = set 2 counter/timer?ode and clock source. should only be altered while the c/t is not in use (i.e., stopped if in counter mode, output and/or interrupt masked if in timer mode). mode clock source 0 0 0 counter external (ip2) 0 0 1counter txca?x clock of channel a transmitter 0 1 0counter txcb?x clock of channel b transmitter 0 1 1counter crystal or external clock (x1/clk) divided by 16 1 0 0timer external (ip2) 1 0 1timer external (ip2) divided by 16* 1 1 0 timer crystal or external clock (x1/clk) 1 1 1timer crystal or external clock (x1/clk) divided by 16 ip change-of-state visible in isr (bits 3, 2, 1, 0) 0 = disabled 1 = enabled ip delta (change-of-state) (bits 7,6,5,4). 0 = no 1 = yes ip level (bits 3,2,1,0). 0 = low 1 = high auxiliary control register (acr) 76543210 brg set select counter/timer ip3 change visible in isr ip2 change visible in isr ip1 change visible in isr ip0 change visible in isr input port change register (ipcr) 76543210 ip3 delta ip2 delta ip1 delta ip0 delta ip3 level ip2 level ip1 level ip0 level programming and register descriptions 4-12 mc68hc681 user? manual motorola 4 all bits 0 = this interrupt source is not active 1 = this interrupt source is active all bits 0 = mask this interrupt source 1 = allow this interrupt source to assert irq * bit seven has no external pin. upon reading the input port, bit seven will always be read as a one ? bit six has no external pin. upon reading the input port, bit six will reflect the current logic level of iack interrupt status register (isr) 76543210 input port change delta break b rxrdyb/ ffullb txrdyb counter/ timer ready delta break a rxrdya/ ffulla txrdya interrupt mask register (imr) 76543210 input port change delta break b rxrdyb/ ffullb txrdyb counter/ timer ready delta break a rxrdya/ ffulla txrdya counter/timer upper register (ctur) 76543210 c/t[15] c/t[14] c/t[13] c/t[12] c/t[11] c/t[10] c/t[9] c/t[8] counter/timer lower register (ctlr) 76543210 c/t[7] c/t[6] c/t[5] c/t[4] c/t[3] c/t[2] c/t[1] c/t[0] interrupt vector register (ivr) 76543210 ivr[7] ivr[6] ivr[5] ivr[4] ivr[3] ivr[2] ivr[1] ivr[0] input port 76543210 * ? ip5 ip4 ip3 ip2 ip1 ip0 programming and register descriptions motorola mc68hc681 user? manual 4-13 4 4.3 register description the following paragraphs provide a detailed description of each register and its function. 4.3.1 channel a mode register 1 (mr1a) the channel a mode register one (mr1a) is accessed when the channel a mode register pointer points to mr1. the pointer is set to mr1 by reset or by a "set pointer" command applied via command register a. after reading or writing mr1a, the pointer will point to channel a mode register two (mr2a). 4.3.1.1 channel a receiver ready-to-recieve control ?mr1a[7]. this bit allows the parallel output op0 to be used as a ready-to-receive indicator (rtra), controlled by the channel a receiver. op0 must first be asserted by setting opr[0]. mr1a[7] = 1 causes rt ra to be negated on receipt of a valid start bit if the channel a fifo is full. rt ra will be reasserted when an empty fifo position is available. this feature can be used for flow control to prevent overrun in the receiver by using the rt ra output signal to control the clear-to-send cts input of the transmitting device. 4.3.1.2 channel a receiver-interrupt select - mr1a[6]. this bit selects either the channel a receiver-ready status (rxrdy) or the channel a fifo full status (ffull) to be used for cpu interrupts. it also causes the selected bit to be output on the parallel output op4 if op4 is programmed as an interrupt output via the output port configuration register (opcr). 4.3.1.3 channel a error mode select - mr1a[5]. this bit selects the operating mode of the three fifo status bits (framing error (fe), parity error (pe), and received break (rb)) for channel a. in the "character" mode, status provided in the status register is given on a character-by-character basis and applies only to the character at the top of the fifo. in the "block" mode, the status provided in the status register for these bits is the accumulation (logical or) of the status for all characters coming to the top of the fifo since the last reset error status command for channel a was issued. 4.3.1.4 channel a parity mode select - mr1a[4:3]. if "with parity" or "force parity" is selected, a parity bit is added to the transmitted character and the receiver performs a parity check on incoming data. mr1a[4:3] = 11 selects channel a to operate in the multidrop mode as described in section 3.4 multidrop mode . 4.3.1.5 channel a parity type select - mr1a[2]. this bit selects the parity type (odd or even) in "with parity" mode; the polarity of the forced parity bit in "force parity" mode; or the state of the address/data tag bit in ?ultidrop?mode. it has no effect in "no parity" mode. 4.3.1.6 channel a bits-per-character select - mr1a[1:0]. this field selects the number of data bits per character to be transmitted and received. the character length does not include the start, parity, and stop bits. programming and register descriptions 4-14 mc68hc681 user? manual motorola 4 4.3.2 channel a mode register 2 (mr2a) the channel a mode register two (mr2a) is accessed when the channel a mode register pointer points to mr2, which occurs after any access to channel a mode register one (mr1a). accesses to mr2a do not change the pointer. 4.3.2.1 channel a mode select - mr2a[7:6]. each channel of the duart can operate in one of four modes: normal, automatic echo, local loopback, or remote loopback. mr2a[7:6] = 00 is the normal mode, with the transmitter and receiver operating independently. mr2a[7:6] = 01 places the channel in the automatic echo mode, which automatically retransmits the received data. the following conditions are true while in the automatic-echo mode: received data is reclocked and retransmitted on the channel a transmitter serial-data output. the receive clock is used for the transmitter. the receiver must be enabled, but the transmitter need not be enabled. the channel a transmitter ready and transmitter empty status bits are inactive. the received parity is checked, but is not recalculated for transmission; i.e., the transmitted parity bit is as received. character framing is checked but the stop bits are retransmitted as received. a received break is echoed as received until the next valid start bit is detected. cpu-to-receiver communication continues normally, but the cpu-to-transmitter link is disabled. two diagnostic modes can also be configured. mr2a[7:6] = 10 selects the first of these, the local- loopback mode. in this mode the transmitter output is internally connected to the receiver input. the transmit clock is used for the receiver. the channel a transmitter serial-data output is held high. the channel a receiver serial-data input is ignored. the transmitter must be enabled, but the receiver need not be enabled. cpu-to-transmitter and receiver communications continue normally. programming and register descriptions motorola mc68hc681 user? manual 4-15 4 the second diagnostic mode is the remote-loopback mode, selected by mr2a(7:6] = 11. received data is reclocked and retransmitted on the channel a transmitter serial-data output. the receive clock is used for the transmitter. received data cannot be read by the local cpu and the error status conditions are inactive. the received parity is not checked and is not recalculated for transmission; i.e., the transmitted parity bit is as received. the receiver must be enabled. character framing is not checked, and the stop bits are retransmitted as received. a received break is echoed as received until the next valid start bit is detected. switching between modes should be done only while the channel is disabled. 4.3.2.2 channel a transmitter request-to-send control - mr2a[5]. this bit controls the negation of the channel a transmitter request-to-send (rtsa ) parallel output (op0) by the transmitter. op0 must be asserted before each message by setting opr[0]. mr2a[5] = 1 causes opr[0] to be cleared automatically one bit time after the characters in the channel a transmit shift register and the transmit holding register, if any, are completely transmitted, including the programmed number of stop bits, and the transmitter is disabled. this feature can indicate the end of a message as follows: 1. program the duart for the automatic-reset mode: mr2a[5] = 1. 2. enable the transmitter. 3. assert channel a transmitter request-to-send control: opr[0] = 1. 4. send the message. 5. disable the transmitter. the transmitter can be disabled any time after the last character has been loaded into the transmit holding register. note, however, that disabling the transmitter forces the txrdy and txemt status bits in the status register to be inactive. if it is necessary to know when the last character transmission is complete, do not disable the transmitter until transmission is complete, as signalled by txemt. in the mc68681, if the transmitter was disabled after transmission was complete, rts would not be negated. this is not true in the mc68hc681. 6. the last character will be transmitted and opr[0] will be cleared one bit time after the last stop bit, causing the channel a transmitter request-to-send control to be negated. note that in this mode, a character in the holding register at the time of the disable command is not held back. in the mc68681, if (1) clear-to-send control was enabled (see paragraph 4.3.2.3), (2) the transmitter was disabled with a character in the holding register, and (3) cts was negated at the time of the disable command, the character in the holding register would not be sent, even if cts was later asserted. this is not true in the mc68hc681.) programming and register descriptions 4-16 mc68hc681 user? manual motorola 4 4.3.2.3 channel a clear-to-send control - mr2a[4]. if this bit is zero, channel a clear-to-send control (ctsa ) has no effect on the transmitter. if this bit is a one, the transmitter checks the state of ctsa (ip0) each time it is ready to send a character. if ip0 is asserted (low), the character is transmitted. if it is negated (high), the channel a transmitter serial-data output remains in the marking state and the transmission is delayed until ctsa goes low. changes of ctsa while a character is being transmitted do not affect the transmission of that character. 4.3.2.4 channel a stop bit length select - mr2a[3:2]. this field programs the number of stop bits appended to transmitted characters. one, one-and-a-half (async mode only), or two stop bits can be programmed for any character length. in all cases, the receiver checks only for a "mark" condition at the center of the first stop bit position (one bit time after the last data bit, or after the parity bit if parity is enabled). 4.3.3 channel b mode register 1 (mr1b) the channel b mode register one (mr1 b) is accessed when the channel b mode register pointer points to mr1. the pointer is set to mr1 by reset or by a "set pointer" command applied via command register b. after reading or writing mr1b, the pointer will point to channel b mode register two (mr2b). the bit definitions for this register are identical to the bit definitions for mr1a, except that all control actions apply to the channel b receiver and transmitter and their corresponding inputs and outputs. 4.3.4 channel b mode register 2 (mr2b) the channel b mode register two (mr2b) is accessed when the channel b mode register pointer points to mr2, which occurs after any access to channel b mode register one (mr1 b). accesses to mr2b do not change the pointer. the bit definitions for this register are identical to the bit definitions for mr2a, except that all control actions apply to the channel b receiver and transmitter and their corresponding inputs and outputs. 4.3.5 channel a clock-select register (csra) in the paragraphs below, acr[7] controls the set of available baud rates. 4.3.5.1 channel a receiver clock select - csra[7:4]. this field selects the baud-rate clock for the channel a receiver from the set of available baud rates. the receiver clock is always 16 times the baud rate given in the table except for csra[7:4] = 1111, when an external 1x clock is used. when csra[7:5] = 111, the receiver uses the external clock connected to parallel input ip4. 4.3.5.2 channel a transmitter clock select - csra[3:0]. this field selects the baud rate clock for the channel a transmitter from the set of available baud rates. the transmitter clock is always 16 times the baud rate given in the table except for csra[3:0] = 1111, when an external 1x clock is used. when csra[3:1] = 111, the external clock connected to parallel input ip3 is used by the transmitter. programming and register descriptions motorola mc68hc681 user? manual 4-17 4 4.3.6 channel b clock-select register (csrb) the bit definitions for this register are identical to those for csra, except that all control actions apply to the channel b receiver and transmitter and their corresponding inputs and outputs. 4.3.6.1 channel b receiver clock select - csrb[7:4]. when csrb[7:5] = 111, the receiver uses the external clock connected to parallel input ip2. 4.3.6.2 channel b transmitter clock select - csrb[3:0]. when csrb[3:1] = 111, the transmitter uses the external clock connected to parallel input ip5. 4.3.7 channel a command register (cra) the command(s) to be issued are encoded in the data value written to the command register address. multiple commands can be specified in a single write to cra provided the commands are nonconflicting; e.g., the "enable transmitter" and "reset transmitter" commands cannot be specified in a single command word. 4.3.7.1 cra[7]. this bit is not used and may be set to either zero or one. 4.3.7.2 channel a miscellaneous commands - cra[6:4]. the encoded value of this field specifies a single command as follows: cra[6:4] command 0 0 0 no command. 0 0 1 reset mode register pointer . this command causes the channel a mode register pointer to point to mode register one. 0 1 0 reset receiver . this command resets the channel a receiver. the receiver is immediately disabled, the rxrdy and ffull bits in the sra are cleared, and the rxfifo pointer is reinitialized. all other registers are unaltered. this command should be used in lieu of the receiver disable command whenever the receiver configuration is to be changed, as it places the receiver in a guaranteed known state. 0 1 1 reset transmitter . this command resets the channel a transmitter. the transmitter is immediately disabled and the txrdy and txemt bits in the sra are cleared. all other registers are unaltered. this command should be used in lieu of the transmitter disable command whenever the transmitter configuration is to be changed, as it places the receiver in a guaranteed known state. 1 0 0 reset error status . this command clears the channel a received break (rb), parity error (pe), framing error (fe), and overrun error (oe) flags in the status register (sra[7:4]). this command is used in the character mode to clear oe status (rb, pe, and fe bits will also be cleared) and is used in the block mode to clear all error status flags after a block of data has been received. programming and register descriptions 4-18 mc68hc681 user? manual motorola 4 4.3.7.3 channel a transmitter commands - cra[3:2]. the encoded value of this field specifies a single command for the transmitter as follows: 4.3.7.4 channel a receiver commands - cra[1:0]. the encoded value of this field specifies a single command for the receiver as follows: 1 0 1 reset channel a break change interrupt. this command causes the channel a break detect change bit in the interrupt status register (isr[2]) to be cleared to zero. 1 1 0 start break . this command forces the channel a transmitter serial-data output (txda) low (spacing). if the transmitter is empty, the start of the break condition will be delayed up to two bit times. if the transmitter is active, the break begins when transmission of the character is completed. if a character is in the transmit holding register, the start of the break will be delayed until that character 1 1 1 stop break . the channel a transmitter serial-data output (txda) line will go high (marking) within two bit times. txda will remain high for one bit time before the next character, if any, is transmitted. note: the error bits must actually be cleared before reading the last character of the block, unless it can be guaranteed that no more characters are in the fifo after the last character of the current block. cra[3:2] command 0 0 no action is taken . the transmitter stays in its present mode. if the transmitter was enabled it remains enabled, if disabled it remains disabled. 0 1 enable transmitter . this command enables operation of the channel a transmitter. 1 0 disable transmitter . this command terminates transmitter operation and resets the transmitter-ready and transmitter-empty status bits. however, if a character is being transmitted when the transmitter is disabled, the transmission of the character is completed before assuming the inactive state. 1 1 illegal command; do not use. cra[1:0] command 0 0 no action is taken . the receiver stays in its present mode. if the receiver was enabled it remains enabled, if disabled it remains disabled. 0 1 enable receiver . this command enables operation of the channel a receiver. if the duart is not in the multidrop mode, this command also forces the receiver into the search-for-start-bit state. 1 0 disable receiver . this command terminates operation of the receiver immediately - a character being received, or waiting in the shift register for an opening in the receive fifo, will be lost. the command has no effect on the receiver status bits or any other control register. if the duart has been programmed to operate in the local loopback or multidrop mode, the receiver operates even if it is disabled. refer to section 3 operation for further information. 1 1 illegal command; do not use. cra[6:4] command programming and register descriptions motorola mc68hc681 user? manual 4-19 4 4.3.8 channel b command register (crb) the bit definitions for this register are identical to those for cra, except that all control actions apply to the channel b receiver and transmitter and their corresponding inputs and outputs. 4.3.9 channel a status register (sra) 4.3.9.1 channel a received break - sra[7]. this bit indicates an all-zero character of the programmed length has been received without a stop bit. this bit is valid only when the rxrdy bit is set (sra[0] = 1). only a single fifo position is occupied when a break is received; additional entries to the fifo are inhibited until the channel a receiver serial data input line returns to the marking state. the break-detect circuitry can detect a break that starts in the middle of a received character; however, the break condition must persist completely through the end of the current character and the next character time to be recognized. (the mc68681 incorrectly signalled a break if the data bits and stop bit were 0, but the parity bit was 1. this is not true in the mc68hc681.) 4.3.9.2 channel a framing error - sra[6]. this bit (when set) indicates that a stop bit was not detected when the corresponding data character in the fifo was received. the stop bit check is made in the middle of the first stop bit position. this bit is valid only when the rxrdy bit is set (sra[0] = 1). framing error and break are exclusive: at least one data bit and/or the parity bit must have been a 1 to signal a framing error. after a framing error, the receiver does not wait for the line to return to the marking state (high); if the line remains low for 1/2 a bit time after the stop bit sample (that is, the nominal end of the first stop bit), the receiver treats it as the beginning of a new start bit. 4.3.9.3 channel a parity error - sra[5]. this bit becomes set when the "with parity" or "force parity" mode is programmed by mode register one and the corresponding character in the fifo is received with incorrect parity. in the multidrop mode, the parity error bit position stores the received address/data bit. this bit is valid only when the rxrdy bit is set (sra[0] = 1). 4.3.9.4 channel a overrun error - sra[4]. this bit (when set) indicates one or more characters in the received data stream have been lost. it becomes set on receipt of a valid start bit when the fifo is full and a character is already in the receive shift register waiting for an empty fifo position. when this occurs, the character in the receive shift register (and its break detect, parity error, and framing error status, if any) is lost. a reset error status command clears this bit. 4.3.9.5 channel a transmitter empty - sra[3]. this bit will be set when the channel a transmitter underruns; i.e., both the transmit holding register and the transmit shift register are empty. it is set after transmission of the last stop bit of a character if no character is in the transmit holding register awaiting transmission. it is cleared when the cpu loads the transmit holding register or when the transmitter is disabled. programming and register descriptions 4-20 mc68hc681 user? manual motorola 4 4.3.9.6 channel a transmitter ready - sra[2]. this bit (when set) indicates that the transmit holding register is empty and ready to be loaded with a character. transmitter ready is set when the character is transferred to the transmit shift register. this bit is cleared when the the cpu loads the transmit holding register, or when the transmitter is disabled. 4.3.9.7 channel a fifo full - sra[1]. this bit is set when a character is transferred from the receive shift register to the receiver fifo and the transfer fills the fifo; i.e., all three fifo holding register positions are occupied. it is cleared when the cpu reads the receiver buffer, unless a fourth character is in the receive shift register waiting for an empty fifo slot. 4.3.9.8 channel a receiver ready - sra[0]. this bit indicates that one or more character(s) has been received and is waiting in the fifo for the cpu to read it. it is set when the first character is transferred from the receive shift register to the empty fifo, and cleared when the cpu reads the receiver buffer, if there are no more characters in the fifo after the read. 4.3.10 channel b status register (srb) the bit definitions for this register are identical to those for sra, except the status applies to the channel b receiver and transmitter and their corresponding inputs and outputs. 4.3.11 output port configuration register (opcr) this register individually configures each bit of the 8-bit parallel output port for general- purpose use or an auxiliary function serving the communication channels. 4.3.11.1 op7 output select - opcr[7]. this bit programs the parallel output op7 to provide either the complement of opr[7] or the channel b transmitter interrupt output, which is the complement of isr[4] (not masked by the interrupt mask register). when configured for the channel b transmitter interrupt, op7 acts as an open-collector output. 4.3.11.2 op6 output select - opcr[6]. this bit programs the parallel output op6 to provide either the complement of opr[6] or the channel a transmitter interrupt output, which is the complement of isr[0] (not masked by the interrupt mask register). when configured for the channel a transmitter interrupt, op6 acts as an open-collector output. 4.3.11.3 op5 output select - opcr[5]. this bit programs the parallel output op5 to provide either the complement of opr[5] or the channel b receiver interrupt output, which is the complement of isr[5] (not masked by the interrupt mask register). when configured for the channel b receiver interrupt, op5 acts as an open-collector output. 4.3.11.4 op4 output select - opcr[4]. this bit programs the parallel output op4 to provide either the complement of opr[4] or the channel a receiver interrupt output, which is the complement of isr[1] (not masked by the interrupt-mask register). when configured for the channel a receiver interrupt, op4 acts as an open-collector output. programming and register descriptions motorola mc68hc681 user? manual 4-21 4 4.3.11.5 op3 output select - opcr[3:2]. this field programs the parallel output op3 to provide one of the following: 4.3.11.6 op2 output select - opcr[1:0]. this field programs the parallel output op2 to provide one of the following: 4.3.12 output port register - opr[7:0] these bits contain the complement of the logic levels output at the output port pins (op7- opo). customers can set these register bits by performing a write to the bit set command address, with data specifying the bits to be set (one equals set, zero equals no change). customers can clear these register bits by performing a write to the bit reset command address, with data specifying the bits to be cleared (one equals reset, zero equals no change). 4.3.13 auxiliary control register (acr) 4.3.13.1 baud-rate generator set select - acr[7]. this bit selects the set of baud-rate generator outputs available for use by the channel a and b receivers and transmitters. baud-rate generator characteristics are given in table 4-5. opcr[3:2] op3 function 0 0 complement of opr[3]. 0 1 counter/timer output, open-collector. in counter mode (acr[6]=0), op3 is the complement of isr[3] (not masked by the interrupt mask register). in timer mode (acr[6]=1), this output is a square wave at the programmed frequency. because the timer cannot be stopped, opcr[3:2] should be cleared until the timer has been programmed for the desired operation. 1 0 1x bit-rate clock of the channel b transmitter, which is the clock that shifts the transmitted data. if data is not being transmitted, a free-running 1x clock is output. 1 1 1x bit-rate clock of the channel b receiver, which is the clock that samples the received data. if data is not being received, a free-running 1x clock is output. opcr[1:0] op2 function 0 0 complement of opr[2]. 0 1 16x bit-rate clock of the channel a transmitter. this is the clock selected by csra[3:0] and will be a 1x clock if csra[3:0] = 1 1 1 1. 1 0 1x bit-rate clock of the channel a transmitter, which is the clock that shifts the transmitted data. a free running 1x clock is always output in this mode. if data is not being transmitted, a free-running 1x clock is output. 1 1 1x bit-rate clock of the channel a receiver, which is the clock that samples the received data. a free running 1x clock is always output in this mode. if data is not being received, a free-running 1x clock is output. programming and register descriptions 4-22 mc68hc681 user? manual motorola 4 4.3.13.2 counter/timer mode and clock source select ?acr[6:4]. this field selects the operating mode of the counter/timer and its clock source as shown in table 4-4. 4.3.13.3 ip3, ip2, ip1, and ip0 change-of-state interrupt enable ? acr[3:0]. these four bits are logically anded with ipcr[7:4], and the results are ored to produce isr[7]. 4.3.14 input port change register (ipcr) 4.3.14.1 ip3, ip2, ip1, and ip0 change of state - ipcr[7:4]. these bits are set at 25-50 microseconds, which occurs at their respective input pins. they are cleared when the cpu reads the input port change register. 4.3.14.2 ip3, ip2, ip1, and ip0 current state ?ipcr[3:0]. these bits provide the current state of their respective inputs. the information reflects the state of the input pins at the time the input port change register is read. 4.3.15 interrupt status register (isr) this register provides the status of all potential interrupt sources. the contents of this register are logically anded with the contents of the interrupt mask register, and the results are nored to produce the irq output. all active interrupt sources are visible by reading the isr, regardless of the contents of the interrupt mask register. reading the isr has no effect on any interrupt source; each active interrupt source must be cleared in a source-specific fashion to clear the isr. all interrupt sources are cleared when the duart is reset. table 4-5. baud-rate generator characteristics crystal or clock = 3.6864 mhz nominal rate (baud) actual 16x clock (khz) error (percent) nominal rate (baud) actual 16x clock (khz) error (percent) 50 0.8 0 1200 19.2 0 75 1.2 0 1800 28.8 0 100 1.759 -0.069 2000 32.056 0.175 134.5 2.153 0.059 2400 38.4 0 150 2.4 0 4800 76.8 0 200 3.2 0 7200 1115.2 0 300 4 8 0 9600 153.6 0 600 9.6 0 19.2k 307.2 0 1050 16.756 -0.260 38.4k 614.4 0 programming and register descriptions motorola mc68hc681 user? manual 4-23 4 4.3.15.1 input port change status - isr[7]. this bit is a one when a change of state has occurred at the ip0, ip1, ip2, or ip3 inputs and that event has been enabled to cause an interrupt by the programming of acr[3:0]. this bit is cleared when the cpu reads the input port change register. 4.3.15.2 channel b change in break ?isr[6]. this bit (when set) indicates that the channel b receiver has detected the beginning or the end of a break condition. it is reset when the cpu issues a channel b reset break change interrupt command. 4.3.15.3 channel b receiver ready or fifo full ?isr[5]. the function of this bit is programmed by mr1b[6]. if programmed as receiver ready, it is a copy of the channel b status register rxrdy bit (srb[0]). if programmed as fifo full, it is a copy of the channel b status register ffull bit (srb[1]). 4.3.15.4 channel b transmitter ready ?isr[4]. this bit is a duplicate of the channel b status register transmitter ready bit (srb[2]). 4.3.15.5 counter/timer ready ?isr[3]. in counter mode, this bit is set when the counter reaches terminal count. in timer mode, this bit is set each time the timer output switches from low to high (every other time that the c/t reaches terminal count). (in both the mc68681 and the mc68hc681, a timer-start command forces the timer output high. in the mc68681, if this caused a low-to-high transition of the timer output, this bit would be set. this is not true in the mc68hc681.) in either mode, the bit is cleared by a c/t stop command. 4.3.15.6 channel a change in break ?isr[2]. this bit is the channel a equivalent of isr[6]. 4.3.15.7 channel a receiver ready or fifo full ?isr[1]. this bit is the channel a equivalent of isr[5]. 4.3.15.8 channel a transmitter ready ?isr[0]. this bit is the channel a equivalent of isr[4]. 4.3.16 interrupt mask register (imr) this register selects which bits in the interrupt status register can cause an interrupt output. if a bit in the interrupt status register is a one and the corresponding bit in this register is also a one, the irq output will be asserted. if the corresponding bit in this register is a zero, the state of the bit in the interrupt status register has no effect on the irq output. note that the interrupt mask register does not mask the programmable interrupt outputs op7 through op3 or the value read from the interrupt status register. programming and register descriptions 4-24 mc68hc681 user? manual motorola 4 4.3.17 count registers (cur and clr) the count upper register (cur) and count lower register (clr) hold the most-significant byte and the least-significant byte, respectively, of the current counter value. these registers should only be read when the c/t is in counter mode and the counter is stopped. see section 3.5 counter/timer for additional information. 4.3.18 counter/timer preload registers (ctur and ctlr) the c/t upper register (ctur) and c/t lower register (ctlr) hold the most-significant byte and eight least-significant bytes, respectively, of the preload value to be used by the c/t in either counter or timer mode. the minimum value that can be loaded into the concatenation of ctur with ctlr is 0001 16 . note that ctur and ctlr are write-only registers and cannot be read by the cpu. 4.3.19 interrupt vector register (ivr) this register contains the interrupt vector. when the duart responds to a valid interrupt acknowledge (iack ) cycle, the contents of this register are placed on the data bus. at reset, this register will contain 0f 16 , which is the m68000 exception vector assignment for uninitialized interrupt vectors. motorola mc68hc681 user? manual 5-1 5 section 5 electrical specifications 5.1 absolute maximum ratings 5.2 thermal characteristics 5.3 power considerations the average chip-junction temperature, t j , in c can be obtained from: t j = t a + (p d q ja ) (1) where: t a = ambient temperature, c q ja = package thermal resistance, junction-to-ambient, c/w p d = p int + p i/o p int = i cc x v cc , watts - chip internal power p i/o = power dissipation on input and output pins - user determined for most applications p i/o < p int and can be neglected. an approximate relationship between p d and t j (if p i/o is neglected) is: p d = k ? (t j + 273 c) (2) solving equations 1 and 2 for k gives: k = p d (t a + 273 c) + q ja p d 2 (3) rating symbol value unit this device contains circuitry to protect the inputs against damage due to high static voltages or electric fields; however, it is advised that normal precautions be taken to avoid application of any voltage higher than maximum-rated voltages to this high-impedance circuit. reliability of operation is enhanced if unused inputs are tied to an appropriate logic voltage level (e.g., either gnd or v cc ). supply voltage v cc -0.5 to + 6.0 v input voltage v in -0.5 to + 6.0 v operating temperature range t a 0 to + 70 c storage temperature t stg -65 to + 150 c characteristic symbol value symbol value rating thermal resistance (still air) plastic, type fn type p q ja 45 50 q jc 22 25 c/w note: estimate electrical specifications 5-2 mc68hc681 user? manual motorola 5 where k is a constant pertaining to the particular part. k can be determined from equation (3) by measuring p d (at equilibrium) for a known t a . using this value of k the values of p d and t j can be obtained by solving equations (1) and (2) iteratively for any value of t a . the total thermal resistance of a package ( q ja ) can be separated into two components, q jc and q ca , representing the barrier to heat flow from the semiconductor junction to the package (case) surface ( q jc ) and from the case to the outside ambient ( q ca ). these terms are related by the equation: q ja = q jc + q ca (4) q jc is device-related and cannot be influenced by customers. however, q ca is customer- dependent and can be minimized by such thermal management techniques as heat sinks, ambient air cooling, and thermal convention. thus, good thermal management on the part of the customer can significantly reduce q ca so that q ja approximately equals q jc . substitution of q jc for q ja in equation (1) will result in a lower semiconductor junction temperature. values for thermal resistance presented in this data sheet, unless estimated, were derived using the procedure described in motorola reliability report 7843, "thermal resistance measurement method for mc68xx microcomponent devices", and are provided for design purposes only. thermal measurements are complex and dependent on procedure and setup. customer-derived values for thermal resistance may differ. 5.4 dc electrical characteristics t a = 0 c to 70 c, v cc = 5.0 v 5% all voltage measurements are referenced to ground (gnd). characteristic symbol min max unit input high voltage, except x1 v ih 2.0 v input high voltage, x1 v ih 4.0 v input low voltage v il 0.8 v output high voltage, except open-collector outputs (i oh = -) v oh 2.4 v output low voltage (i ol = ) v ol 0.6 v input leakage current (v in = 0 to v cc )i il -5 5 m a data bus hi-z leakage current (v out = 0 to v cc )i ll -5 5 m a open-collector output leakage current (v out = 0 to v cc )i oc -5 5 m a power supply current i cc 25 ma capacitance (v in = 5 v, ta = 25 c, f = 1 mhz) c in ?15pf x1 low input current v in = 0, x2 floated i x1l -10 ? ma x1 high lnput current v in = v cc , x2 floated i x1h ?10ma electrical specifications motorola mc68hc681 user? manual 5-3 5 5.5 ac electrical characteristics t a = 0 c to 70 c, v cc = 5.0 v 5% all voltage measurements are referenced to ground (gnd). for testing, all input signals except x1 swing between 0.4 v and 2.4 v with a maximum transition time of 20 ns. for x1, the swing is between 0.4 v and 4.4 v. all time measurements are referenced at input and output voltages of 0.8 v and 2.0 v as appropriate. test conditions for non-interrupt outputs: c l = pf, r l = w to v cc . test conditions for interrupt outputs: c l = pf, r l = w to v cc 5.5.1 clock timing figure 5-1. clock timing characteristic symbol min max unit x1 frequency* f clk 0 4.0 mhz x1 high or low time t clk 100 ns counter/timer clock frequency f ctc 0 16.0 mhz counter/timer clock high or low time t ctc 25 ns receiver clock frequency (rxc) 16x clock 1x clock f rx 0 0 4.0 1.0 mhz receive clock (rxc) high or low time t rx 100 ns transmitter clock frequency (txc) 16x clock 1x clock f tx 0 0 4.0 1.0 mhz transmit clock (txc) high or low t tx 100 ns clock rise time t r ?0ns clock fall time t f ?0ns note: * for the baud-rate generator to generate the standard baud rates shown in section 4.2 register bit formats , the x1 frequency should be set to 3.6864 mhz or a 3.6864 mhz crystal should be connected across pins x1 and x2. t f t r t clk t ctc t rx t tx t clk t ctc t rx t tx x1 c/t clk rxc txc electrical specifications 5-4 mc68hc681 user? manual motorola 5 5.5.2 reset timing figure 5-2. reset timing 5.5.3 read and write bus cycle timing characteristic symbol min max unit reset pulse width* t res 1.0 m s note: * the mc68hc681 does not require a clock for correct reset characteristic symbol min max unit cs setup time to x1 high 1 t csc 90 ns rs1-rs4 setup time to cs asserted t rss 10 ns r/w setup time to cs asserted t rws 10 ns cs pulse width asserted 2 t cswl 205 ns data valid from cs asserted t dd 175 ns dtack asserted from x1 high t dcr 125 ns cs negated from dtack asserted 2 t csd 0 ns rs1-rs4 hold time from cs negated t rsh 0 ns r/w hold time from cs negated t rwh 0 ns data hold time from cs negated t dh 0 ns data bus floating from cs negated t df 100 ns dtack negated from cs negated t dah 100 ns dtack hi-z from cs negated t dat 125 ns cs pulse width negated t cswh 90 ns data setup time to cs negated 3 t dscs 100 ns dtack asserted from x1 high t dcw 125 ns data hold time from cs negated t dh 0 ns notes: 1. this speci?ation is only to ensure dtack is asserted with respect to the rising edge of x1 as shown in figure 5-3 and figure 5- 4, not to guarantee operation of the part. if the setup time is violated, dtack may be asserted as shown, or may be asserted one clock cycle later. 2. this speci?ation is only to ensure that dtack will be asserted. if cs is negated before dtack is asserted, dtack may not be asserted. 3. during write cycles, the mc68681 latched data on either the assertion edge of dtack or the negation edge of cs , whichever occurred ?st. this is not true in the mc68hc681: the mc68hc681 always latches write data on the negation edge of cs . reset t res electrical specifications motorola mc68hc681 user? manual 5-5 5 5.5.4 interrupt bus cycle timing characteristic symbol min max unit iack setup time to x1 high 1 t csc 90 ns r/w setup time to iack asserted 2 t rws 10 ns iack pulse width asserted t iawl 205 ns data valid from iack asserted t dd 175 ns dtack asserted from x1 high t dcr 125 ns iack negated from dtack asserted 3 t csd 0 ns r/w hold time from iack negated t rwh 0 ns data hold time from iack negated t dh 0 ns data bus floating from iack negated t df 100 ns dtack negated from iack negated t dah 100 ns dtack hi-z from iack negated t dat 125 ns notes: 1. this speci?ation is only to ensure dtack is asserted with respect to the rising edge of x1 as shown in figure 5-3 and figure 5- 4, not to guarantee operation of the part. if the setup time is violated, dtack may be asserted as shown, or may be asserted one clock cycle later. 2. during iack cycles, the mc68681 ignored r/w ; this is not true in the mc68hc681: r/w must be high on iack cycles. the mc68hc681 ignores iack if r/w is low. 3. this speci?ation is only to ensure that dtack will be asserted. if iack is negated before dtack is asserted, dtack may not be asserted. electrical specifications 5-6 mc68hc681 user? manual motorola 5 figure 5-3. read cycle bus timing figure 5-4. write cycle bus timing x1 rs4?s1 d0-d7 dtack cs r/w t csc t rss t rws t cswl t csd t dat t dd t rsh t rwh t cswh t dh t df t dah t dc x1 rs4?s1 d0-d7 dtack cs r/w t csc t rss t rws t cswl t dh t csd t dscs t rsh t rwh t dah t ds t dat t dcw t cswh electrical specifications motorola mc68hc681 user? manual 5-7 5 figure 5-5. interrupt cycle bus timing 5.5.5 port timing figure 5-6. port timing characteristic symbol min max unit port input setup time to cs asserted t ps 10 ns port 1nput hold time from cs negated t ph 0 ns port output valid from cs negated t pd 400 ns x1/clk d0-d7 * cs and iack should not be asserted simultaneously. dtack iack * irq t csc t iawl t dh t csd t dcr t dd t dah t dat t df t ps cs op7?p0 ip0-ip5 old data new data cs t pd t ph electrical specifications 5-8 mc68hc681 user? manual motorola 5 5.5.6 interrupt reset timing figure 5-7. interrupt reset timing 5.5.7 transmitter timing figure 5-8. transmitter timing characteristic symbol min max unit irq negated or op3-op7 high (when used as interrupts) from cs negated: reset receiver command (rxrdy/ffull interrupt) read rb (rxrdy/ffull interrupt) reset transmitter command (txrdy interrupt) write tb (txrdy interrupt) reset break change interrupt command (delta break interrupt) stop counter/timer command (counter/timer interrupt) read ipcr (input port change interrupt) write imr (clear a mask bit) t ir 300 300 300 300 300 300 300 300 300 ns ns ns ns ns ns ns ns ns characteristic symbol min max unit txd output valid from txc low t txd 350 ns txc low to txd output valid t tcs 150 ns t ir cs (read or write cycle) interrupt output * * irq or op3-op7 when used as interrupt outputs. t tcs txc (input) txc (1x output) txd t txd 1 bit time (1 or 16 clocks) electrical specifications motorola mc68hc681 user? manual 5-9 5 5.5.8 receiver timing figure 5-9. receiver timing characteristic symbol min max unit rxd data setup time to rxc high t rxs 240 ns rxd data hold time from rxc high t rxh 200 ns rxd rxc (1x input) t rxs t rxh electrical specifications 5-10 mc68hc681 user? manual motorola 5 5.5.9 transmitter and receiver operation figure 5-10. transmitter operation c1 c2 c3 c4 c6 ww w w w w w w c1 c2 c3 c4 stop break start break c5 not transmitted c6 break c1 in transmission txdx transmitter enabled txrdy (sr2) cs cts (ip0) rts (op0) 2 1 n manually asserted by bit- set command manually asserted notes: 1. timing shown for mr2(4) = 1 2. timing shown for mr2(5) = 1 3. c = transmit character 4. w = write electrical specifications motorola mc68hc681 user? manual 5-11 5 figure 5-11. receiver operation c6, c7, c8 are lost rxd receiver enabled rxrdy (sr0) ffull (sr1) overrun (sr4) rts (op0) 1 status data status (s) data (d) cs reset by command opr(0) = 1 c4 c3 c5 c6 c7 c8 c1 c2 notes: 1. timing shown for mr1(7) = 1 2. timing shown for opcr(4) = 1 and mr1(6) = 0 3. r = read 4. c = received character n rr r sd r r rr r c1 c2 c3 c4 c5 lost sd sd motorola mc68hc681 user? manual 6-1 6 section 6 mechanical data and ordering information 6.1 pin assignments 6.2 ordering information package type frequency (mhz) temperature order number plastic plcc fn suffix 4.0 0 c to 70 c mc68hc681fn 1 7 18 28 29 640 39 17 nc rs1 ip3 rs2 ip1 rs3 v cc ip4 ip5 iack ip2 nc gnd d7 d5 d3 d1 d6 d4 d2 d0 rs4 ip0 r/w dtack rxdb nc txdb op1 op3 op5 op7 cs reset x2 x1/clk rxda nc txda op0 op2 op4 op6 irq mc68hc681fn mechanical data and ordering information 6-2 mc68hc681 user? manual motorola 6 6.3 package dimensions notes: 1. positional tolerance of leads (d), shall be within 0.25 mm (0.010) at maximum material condition, in relation to seating plane and each other. 2. dimension l to center of leads when formed parallel. 3. dimension b does not include mold flash. notes: 1. datums ?? ?? and ??are determined where top of lead shoulder exits plastic body at mold parting line. 2. dimension g1, true position t o be measured at datum ?? seating plane. 3. dimensions r and u do not include mold flash. allowable mold flash is 0.010 (0.25) per side. 4. dimensioning and tolerancing per ansi y14.5m, 1982. 5. controlling dimension: inch. 6. the package t op may be smaller than the package bott om by up to 0.012 (0.300). dimensions r and u are determined at the outermost extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but including any mismatch between the top and bottom of the plastic body. 7. dimension h does not include dambar protrusion or intrusion. the dambar protrusion(s) shall not cause the h dimension to be greater than 0.037 (0.940). the dambar intrusion(s) shall not cause the h dimension t o be smaller than 0.025 (0.635). n l m d y d k v w 1 44 brk b z u x view d d s l? m 0.007(0.180) n s t s l? m 0.007(0.180) n s t g1 s l? s 0.010 (0.25) n s t k1 f h s l? m 0.007(0.180) n s t z g g1 r a e j view s c s l? m 0.007(0.180) n s t s l? m 0.007(0.180) n s t 0.004 (0.10) t seating plane view s dim min max min max millimeters inches a 0.685 0.695 17.40 17.65 b 0.685 0.695 17.40 17.65 c 0.165 0.180 4.20 4.57 e 0.090 0.110 2.29 2.79 f 0.013 0.019 0.33 0.48 g 0.050 bsc 1.27 bsc h 0.026 0.032 0.66 0.81 j 0.020 0.51 k 0.025 0.64 r 0.650 0.656 16.51 16.66 u 0.650 0.656 16.51 16.66 v 0.042 0.048 1.07 1.21 w 0.042 0.048 1.07 1.21 x 0.042 0.056 1.07 1.42 y 0.020 0.50 z 2 10 2 10 g1 0.610 0.630 15.50 16.00 k1 0.040 1.02 s l? s 0.010 (0.25) n s t s l? m 0.007(0.180) n s t mechanical data and ordering information motorola mc68hc681 user? manual 6-3 6 6.4 pin assignment ?40 pin dual-in-line plastic package 6.5 ordering information package type frequency (mhz) temperature order number plastic p suffix 4.0 0 c to 70 c mc68hc681p d4 op7 ip4 ip5 ip6 ip2 cs txda op4 op6 rs1 ip3 rs2 ip1 rs3 rs4 ip0 w r rxdb txdb op1 v cc d1 d3 d5 d7 gnd 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 22 23 21 op5 op0 op2 irq d6 d2 d0 rxda x1/clk x2 reset op3 mc68hc681p mechanical data and ordering information 6-4 mc68hc681 user? manual motorola 6 6.6 package dimensions ?40 pin dual-in-line package notes: 1. dimension a is datum. 2. positional tolerance for leads: 3. t is seating plane. 4. dimension "l" to center of leads when formed parallel. 5. dimensioning and tolerancing per ansi y14.5, 1973. notes: 1. positional tolerance of leads (d), shall be within 0.25 (0.010) at maximum material condition, in relation to seating plane and each other. 2. dimension l to center of leads when formed parallel. 3. dimension b does not include mold flash. 1 20 40 21 b a c seating plane d f g h k n m j l dim min max min max inches millimeters a 51.69 52.45 2.035 2.065 b 13.72 14.22 0.540 0.560 c 3.94 5.08 0.155 0.200 d 0.36 0.56 0.014 0.022 f 1.02 1.52 0.040 0.060 g 2.54 bsc 0.100 bsc h 1.65 2.16 0.065 0.085 j 0.20 0.38 0.008 0.015 k 2.92 3.43 0.115 0.135 l 15.24 bsc 0.600 bsc m 0 15 0 15 n 0.51 1.02 0.020 0.040 motorola mc68hc681 user? manual a-1 a appendix a MC68HC2681 the MC68HC2681 dual asynchronous receiver/transmitter (duart) is functionally equivalent to the mc68hc681 with some minor differences. the description of the mc68hc681 applies to the MC68HC2681 except for the areas described below. a.1 introduction unlike the mc68hc681, which has an m68000 bus interface, the MC68HC2681 has a general-purpose interface that can be used with both synchronous and asynchronous microprocessors. the device has a multipurpose 7-bit input port and a multipurpose 8-bit output port. these ports can be used as general-purpose i/o ports or can be assigned specific functions (such as clock inputs or status/interrupt outputs) under program control. figure a-1 is a block diagram for the MC68HC2681. a.1.1 interrupt control logic the internal operation of interrupt events and registers is identical to the mc68hc681; however, the mh68hc2681 does not have an iack pin, and therefore does not support interrupt acknowledge bus cycles. the ivr can be written and read but cannot be used to vector the cpu to an interrupt service routine. a.1.2 input port the MC68HC2681 input port pins and associated registers are identical to those of the mc68hc681, with the exception of an extra pin (ip6) and the channel b receiver clock select programming (csrb(7-4)). a.2 signal description table a-1, like that for the mc68hc681 found in section 2 signal descriptions , provides a quick reference in determining a signal? pin number, its use as an input or output, whether it is active high or low, and the section containing more information about its operation. the signal description given for the mc68hc681 applies to the MC68HC2681 except for the areas described in this appendix. MC68HC2681 a-2 mc68hc681 user? manual motorola a . figure a-1. MC68HC2681 block diagram crystal oscillator baud rate generator clock selectors counter/ timer timing logic internal control logic two- character tx buffer four-character rx buffer channel a two-character tx buffer four-character rx buffer channel b reset rs1-rs4 change-of- state detectors (4) input port data bus buffer interrupt control logic output port external interface txda rxda txdb rxdb ip0-ip6 op0-op7 x1/clk x2 processor interface d0-d7 vcc gnd internal data bus irq r w c MC68HC2681 motorola mc68hc681 user? manual a-3 a table a-1. MC68HC2681 signal summary signal name mnemonic pin no. in/out active state refer to para. no. p pkg. fn pkg. power supply ( + 5 v) v cc 40 44 in high 2.1 ground gnd 20 22 in low 2.1 crystal input or external clock x1 32 36 in 2.2 crystal output x2 33 37 out 2.3 reset reset 34 38 in high a.2.1 chip select cs 35 39 in low a.2.2 write strobe w 8 9 in low a.2.3 read strobe r 9 10 in low a.2.4 register-select bus bit 4 rs4 6 7 in/out high 2.8 register-select bus bit 3 rs3 5 6 in high 2.8 register-select bus bit 2 rs2 3 4 in high 2.8 register-select bus bit 1 rs1 1 2 in high 2.8 bidirectional-data bus bit 7 d7 19 21 in/out high 2.9 bidirectional-data bus bit 6 d6 22 25 in/out high 2.9 bidirectional-data bus bit 5 d5 18 20 in/out high 2.9 bidirectional-data bus bit 4 d4 23 26 in/out high 2.9 bidirectional-data bus bit 3 d3 17 19 in/out high 2.9 bidirectional-data bus bit 2 d2 24 27 in/out high 2.9 bidirectionai-data bus bit 1 d1 16 18 in/out high 2.9 bidirectional-data bus bit 0 d0 25 28 in/out high 2.9 interrupt request irq 21 24 out 1 low 2.10 channel a transmitter serial data txda 30 33 out 2.12 channel a receiver serial data rxda 31 35 in 2.13 channel b transmitter serial data txdb 11 13 out 2.14 channel b receiver serial data rxdb 10 11 in 2.15 parallel input 6 ip6 37 41 in a.2.5 parallel input 5 ip5 38 42 in 2.16.1 parallel input 4 ip4 39 43 in 2.16.2 parallel input 3 ip3 2 3 in 2.16.3 parallel input 2 ip2 36 40 in a.2.6 parallel input 1 ip1 4 5 in 2.16.5 parallel input 0 ip0 7 8 in 2.16.6 parallel output 7 op7 15 17 out 2 2.17.1 parallel output 6 op6 26 29 out 2 2.17.2 parallel output 5 op5 14 16 out 2 2.17.3 parallel output 4 op4 27 30 out 2 2.17.4 parallel output 3 op3 13 15 out 2 2.17.5 parallel output 2 op2 28 31 out 2.17.6 parallel output 1 op1 12 14 out 2.17.7 parallel output 0 op0 29 32 out 2.17.8 notes: 1. requires a pull-up resistor. 2. may require a pull-up resistor, depending on its programmed function. MC68HC2681 a-4 mc68hc681 user? manual motorola a a.2.3 reset (reset) operation is identical to the mc68hc681 reset , except it is active high. a.2.4 chip-select (cs ) this active low signal is used in conjunction with r and w to enable data transfers between the cpu and duart. if cs and r are both low, a read cycle occurs; if cs and w are both low, a write cycle occurs. cs by itself does not cause any data transfer. a.2.5 write strobe (w ) this active low signal is used in conjunction with cs to enable data to be written to a duart register. the write occurs at the rising edge of w or cs , whichever occurs first. w by itself does not cause any data transfer. a.2.6 read strobe (r ) this active low signal is used in conjunction with cs to enable data to be read from a duart register. the read occurs at the falling edge of r or cs , whichever occurs last. w by itself does not cause any data transfer. a.2.7 parallel input 6 (ip6) this signal can be used as a general-purpose input or a channel b receiver external clock input (rxcb). when the receiver uses the external clock , the received data is sampled on the rising edge of the clock. a.2.8 parallel input 2 (ip2) this signal can be used as a general-purpose input or a counter/timer (c/t) external clock input. this signal cannot be used as a channel b receiver external clock; ip6 provides that functionality in the MC68HC2681. a.3 programming and register description table a-2 describes the register addresses and address-triggered commands for the MC68HC2681. the detailed description of each register and its function, given for the mc68hc681 in section 4 programming and register descriptions , applies to the MC68HC2681. MC68HC2681 motorola mc68hc681 user? manual a-5 a table a-2. MC68HC2681 register addressing and address-triggered commands rs4 rs3 rs2 rs1 read write 0 0 0 0 mode register a (mr1a, mr2a) mode register a (mr1a, mr2a) 0 0 0 1 status register a (sra) clock select register a (csra) 0 0 1 0 clock select register a 1 (csra) command register a (cra) 0 0 1 1 receiver buffer a (rba) transmit buffer a (tba) 0 1 0 0 input port change register (ipcr) auxiliary control register (acr) 0 1 0 1 interrupt status register (isr) interrupt mask register (imr) 0 1 1 0 counter mode: current msb of counter (cur) counter/ timer upper register (ctur) 0 1 1 1 counter mode: current lsb of counter (clr) counter/timer lower register (ctlr) 1 0 0 0 mode register b (mr1b, mr2b) mode register b (mr1b, mr2b) 1 0 0 1 status register b (srb) clock select register b (csrb) 1 0 1 0 clock select register b 2 (csrb) command register b (crb) 1 0 1 1 receiver buffer b (rbb) transmit buffer b (tbb) 1 1 0 0 interrupt vector registe 2 (ivr) interrupt vector register 2 (ivr) 1 1 0 1 input port (ip) output port configuration register (opcr) 1 1 1 0 start counter command 3 output port register (opr) bit set command 1 1 1 1 stop counter command 3 bit reset command notes: 1. reading from this address is prohibited in the mc2681. 2. this register serves no useful function in the mc2681 or MC68HC2681. 3. address-triggered command. MC68HC2681 a-6 mc68hc681 user? manual motorola a a.4 electrical specifications a.4.9 absolute maximum ratings a.4.10 thermal characteristics a.4.11 dc electrical characteristics t a = 0 c to 70 c, v cc = 5.0 v 5% all voltage measurements referenced to ground (gnd) rating symbol value unit this device contains circuitry to protect the inputs against damage due to high static voltages or electric fields; however, it is advised that normal precautions be taken to avoid application of any voltage higher than maximum-rated voltages to this high- impedance circuit. reliability of operation is enhanced if unused inputs are tied to an appropriate logic voltage: level (either gnd or v cc ). supply voltage v cc -0.5 to + 6.0 v input voltage v in -0.5 to + 6.0 v operating temperature range t a 0 to + 70 c storage temperature t stg -65 to + 150 c characteristic symbol value symbol value rating thermal resistance MC68HC2681 plastic, type fn type p q ja 45 50 q jc 22 25 c/w note: estimate characteristic symbol min max unit input high voltage, except x1 v ih 2.0 v input high voltage, x1 v ih 4.0 v input low voltage v il 0.8 v output high voltage, except open-collector outputs (i oh = - ma) v oh 2.4 v output low voltage i ol = ma) v ol 0.4 v input leakage current (v in = 0 to v cc )i il -5 +5 m data bus hi-z leakage current (v out = 0 to v cc )i ll -5 5 m open-collector output leakage current (v out = 0 to v cc )i oc -5 5 m power supply current i cc ?5ma capacitance (v in = 5 v, t a = 25 c, f = 1 mhz) c in ?5pf x1 low input current v in = 0, x2 floated i x1l -10 ma x1 high input current v in = v cc , x2 floated i x1h ?0ma MC68HC2681 motorola mc68hc681 user? manual a-7 a a.4.12 ac electrical characteristics t a = 0 c to 70 c, v cc = 5.0 v 5% all voltage measurements are referenced to ground (gnd). for testing, all input signals except x1 swing between 0.4 v and 2.4 v with a maximum transition time of 20 ns. for x1, the swing is between 0.4 v and 4.4 v. all time measurements are referenced at input and output voltages of 0.8 v and 2.0 v as appropriate. test conditions for non-interrupt outputs: c l = pf, r l = w to v cc . test conditions for interrupt outputs: c l =pf, r l = w to v cc . a.4.12.1 clock timing . figure a-2. clock timing characteristic symbol min max unit x1 frequency * f clk 0 4.0 mhz x1 high or low time t clk 100 ns counter/timer clock frequency f ctc 0 16.0 mhz counter timer clock high or low time t ctc 25 ns receiver frequency 16x clock 1x clock f rx 0 0 4.0 1.0 mhz receive clock (rxc) high or low time t rx 100 ns transmitter frequency 16x clock 1x clock f tx 0 0 4.0 1.0 mhz transmit clock (txc) high or low time t tx 100 ns clock rise time t r 20 ns clock fall time t f 20 ns note: * for the baud-rate generator to generate the standard baud rates shown in section 4.2 register bit formats , x1 must be 3.6864 mhz t f t r t clk t ctc t rx t tx t t t rx t x1 c/t clk rxc txc clk ctc tx MC68HC2681 a-8 mc68hc681 user? manual motorola a a.4.12.2 reset timing . figure a-3. reset timing a.4.12.3 bus timing . figure a-4. bus timing characteristic symbol min max unit reset pulse width t res 1.0 m characteristic symbol min max unit rs1-rs4 setup to r +cs , w +cs asserted t rss 10 ns rs1-rs4 hold after r +cs , w +cs negated t rsh 0 ns bus cycle (r +cs , w +cs ) width t rw 205 ns inactive time between bus cycles t rwd 200 ns read access time from r +cs asserted t rd 175 ns read data valid after r +cs negated t d 0-ns data tri-state after r +cs negated t dz ?5ns write data setup to w +cs negated t wds 100 ns write data hold after w +cs negated t wdh 10 ns rs1-rs4 setup to r +cs , w +cs asserted t rss 10 ns rs1-rs4 hold after r +cs , w +cs negated t rsh 0 ns reset t res rs1 - rs4 cs r w d0-d7 (read) d0-d7 (write) t rss t rsh t rw t rd t dz t d t wds t wdh t rwd valid valid MC68HC2681 motorola mc68hc681 user? manual a-9 a a.4.12.4 port timing . figure a-5. port timing a.4.12.5 interrupt reset timing . figure a-6. interrupt reset timing characteristic symbol min max unit port input setup time to r asserted t ps 10 ns port input hold time from r negated t ph 0 ns port output valid from w negated t pd 400 ns characteristic symbol min max unit irq negated or op3-op7 high (when used as interrupts) from r or w negated: reset receiver command (rxrdy/ffull interrupt) read rb (rxrdy/ffull interrupt) reset transmitter command (txrdy interrupt) write tb (txrdy interrupt) reset break change interrupt command (delta break interrupt) stop counter/timer command (counter/timer interrupt) read ipcr (input port change interrupt) write imr (clear a mask bit) t ir 300 300 300 300 300 300 300 300 ns ns ns ns ns ns ns ns t ps r op0- op7 ip0- ip6 old data new data w t pd t ph t ir r or w and cs irq or op3-op7 MC68HC2681 a-10 mc68hc681 user? manual motorola a a.4.12.6 transmitter timing figure a-7. transmitter timing a.4.12.7 receiver timing . figure a-8. receiver timing characteristic symbol min max unit txd output valid from txc low t txd 350 ns txc low to txd output valid t tcs 150 ns characteristic symbol min max unit rxd data setup time to rxc high t rxs 240 ns rxd data hold time from rxc high t rxh 200 ns t tcs txc (input) txc (1xoutput) txd t txd 1 bit time (1 or 16 clocks) rxd rxc (1x input) t rxs t rxh MC68HC2681 motorola mc68hc681 user? manual a-11 a . figure a-9. transmitter operation d1 d2 d3 d4 d6 w wwww w ww c1 c2 c3 c4 stop break start break c5 not transmitted c6 break txdx transmitter enabled txrdy (sr2) w cts (ip0) rts (op0) 2 1 n opr(0)=1 notes: 1. timing shown for mr2(4) = 1 2. timing shown for mr2(5) = 1 3. c = transmit character 4. w = write opr(0)=1 MC68HC2681 a-12 mc68hc681 user? manual motorola a . figure a-10. receiver operation d6, d7, d8 are lost rxd receiver enabled rxrdy (sr0) ffull (sr1) overrun (sr4) rts (op0) 1 status data status data status data r reset by command opr(0) = 1 d4 d3 d5 d6 d7 d8 d1 d2 notes: 1. timing shown for mr1(7) = 1 2. timing shown for opcr(4) = 1 and mr1(6) = 0 3. r = read 4. c = received character n rr rr r rr r d1 d2 d3 d4 d5 lost status data rxrdy, ffull MC68HC2681 motorola mc68hc681 user? manual a-13 a . figure a-11. wake-up mode operation 10 c0 1 addr 1 addr 2 a/d a/d a/d master station 1 0 c0 1 0 addr 1 addr 2 a/d a/d a/d a/d a/d peripheral station mr1(2) = 1 w w w w ww mr1(2) = 0 addr2 addr1 mr1(4:3) = 11 mr1(2) = 1 0 receiver enabled rxd txd transmitter enabled txrdy (sr2) w mr1(4?) = 11 addr1 w rrr c0 cs w enable rr rxrdy r status data addr2 status data enable w status data MC68HC2681 a-14 mc68hc681 user? manual motorola a a.5 mechanical data and ordering information a.5. 1 pin assignment ?44 pin plastic leaded chip carrier a.5.2 fn suffix ordering information package type frequency (mhz) temperature order number plastic (fn suffix) 4.0 0 c to 70 ? c MC68HC2681fn 1 7 18 28 29 640 39 17 nc rs1 ip3 rs2 ip1 rs3 v cc ip4 ip5 iack ip2 nc gnd d7 d5 d3 d1 d6 d4 d2 d0 rs4 ip0 r/w dtack rxdb nc txdb op1 op3 op5 op7 cs reset x2 x1/clk rxda nc txda op0 op2 op4 op6 irq MC68HC2681fn MC68HC2681 motorola mc68hc681 user? manual a-15 a a.5.3 fn suffixpackaging dimensions . notes: 1. positional tolerance of leads (0), shall be within 0.25mm(0.010) at maximum material condition, in relation to seating plane and each other. 2. dimension l to center of leads when formed parallel. 3. dimension b does not include mold flash. notes: 1. datums ?? ?? and ??are determined where top of lead shoulder exits plastic body at mold parting line. 2. dimension g1, true position t o be measured at datum ?? seating plane. 3. dimensions r and u do not include mold flash. allowable mold flash is 0.010 (0.25) per side. 4. dimensioning and tolerancing per ansi y14.5m, 1982. 5. controlling dimension: inch. 6. the package t op may be smaller than the package bott om by up to 0.012 (0.300). dimensions r and u are determined at the outermost extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but including any mismatch between the top and bottom of the plastic body. 7. dimension h does not include dambar protrusion or intrusion. the dambar protrusion(s) shall not cause the h dimension to be greater than 0.037 (0.940). the dambar intrusion(s) shall not cause the h dimension t o be smaller than 0.025 (0.635). n l m d y d k v w 1 44 brk b z u x view d d s l? m 0.007(0.180) n s t s l? m 0.007(0.180) n s t g1 s l? s 0.010 (0.25) n s t k1 f h s l? m 0.007(0.180) n s t z g g1 r a e j view s c s l? m 0.007(0.180) n s t s l? m 0.007(0.180) n s t 0.004 (0.10) t seating plane view s dim min max min max millimeters inches a 0.685 0.695 17.40 17.65 b 0.685 0.695 17.40 17.65 c 0.165 0.180 4.20 4.57 e 0.090 0.110 2.29 2.79 f 0.013 0.019 0.33 0.48 g 0.050 bsc 1.27 bsc h 0.026 0.032 0.66 0.81 j 0.020 0.51 k 0.025 0.64 r 0.650 0.656 16.51 16.66 u 0.650 0.656 16.51 16.66 v 0.042 0.048 1.07 1.21 w 0.042 0.048 1.07 1.21 x 0.042 0.056 1.07 1.42 y 0.020 0.50 z 2 10 2 10 g1 0.610 0.630 15.50 16.00 k1 0.040 1.02 s l? s 0.010 (0.25) n s t s l? m 0.007(0.180) n s t MC68HC2681 a-16 mc68hc681 user? manual motorola a a.5.4 pin assignment?40 pin dual-in line plastic package a.5.5 p suffix ordering information package type frequency (mhz) temperature order number plastic (p suffix) 4.0 0 c to 70 ? c MC68HC2681p d4 op7 ip4 ip5 ip6 ip2 cs txda op4 op6 rs1 ip3 rs2 ip1 rs3 rs4 ip0 w r rxdb txdb op1 v cc d1 d3 d5 d7 gnd 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 22 23 21 op5 op0 op2 irq d6 d2 d0 rxda x1/clk x2 reset op3 MC68HC2681p MC68HC2681 motorola mc68hc681 user? manual a-17 a a.5.6 package dimensions ?plastic notes: 1. positional tolerance of leads (d), shall be within 0.25 (0.010) at maximum material condition, in relation to seating plane and each other. 2. dimension l to center of leads when formed parallel. 3. dimension b does not include mold flash. 1 20 40 21 b a c seating plane d f g h k n m j l dim min max min max inches millimeters a 51.69 52.45 2.035 2.065 b 13.72 14.22 0.540 0.560 c 3.94 5.08 0.155 0.200 d 0.36 0.56 0.014 0.022 f 1.02 1.52 0.040 0.060 g 2.54 bsc 0.100 bsc h 1.65 2.16 0.065 0.085 j 0.20 0.38 0.008 0.015 k 2.92 3.43 0.115 0.135 l 15.24 bsc 0.600 bsc m 0 15 0 15 n 0.51 1.02 0.020 0.040 motorola mc68hc681 user? manual i-1 ind e index a acr, 4-21 automatic-echo mode, 3-5 b block diagrams MC68HC2681, a-2 mc68hc681, 1-2 programming, 4-2 c clear-to-send, 3-1 clock sources, 4-5 clr, 4-24 counter mode, 3-6 counter/timer, 3-6 cra, 4-17 crb, 4-19 cs, 2-3 csra, 4-16 csrb, 4-17 ctlr, 4-24 ctur, 4-24 cur, 4-24 d d0?7, 2-4 descriptions programming, 4-1 register, 4-13 dtack, 2-4 e electrical specifications, 5-1 f features mc68hc681, 1-1 formats register bit, 4-6 g gnd, 2-2 i iack, 2-4 imr, 4-23 ip0, 2-4 ip0?p5, 2-4 ip1, 2-5 ip2, 2-5 ip3, 2-5 ip4, 2-5 ip5, 2-5 ipcr, 4-22 irq, 2-4 isr, 4-22 ivr, 4-24 l local-loopback mode, 3-5 looping modes, 3-4 m MC68HC2681 electrical specifications, a-6 mechanical data, a-15 ordering information, a-14 package dimensions 6-4, a-17 programming and register descriptions, a-4 signal description, a-1 MC68HC2681, a-1 index i-2 mc68hc681 user? manual motorola dex mc68hc681 block diagram, 1-2 introduction, 1-1 operation, 3-1 programming and register descriptions, 4-1 signal descriptions, 2-1 mechanical data, 6-1 mode automatic-echo, 3-5 counter, 3-6 local-loopback, 3-5 looping, 3-4 multidrop, 3-5 remote-loopback, 3-5 timer, 3-7 mr1a, 4-13 mr1b, 4-16 mr2a, 4-14 mr2b, 4-16 multidrop mode, 3-5 o op0, 2-5 op0?p7, 2-5 op1, 2-5 op2, 2-6 op3, 2-6 op4, 2-6 op5, 2-6 op6, 2-6 op7, 2-6 opcr, 4-20 operation counter/timer timer mode, 3-7 counter/timer, 3-6 coutner/timer counter mode, 3-6 looping modes automatic-echo, 3-5 local-loopback, 3-5 remote loopback, 3-5 looping modes, 3-4 multidrop mode, 3-5 receiver, 3-2 transmitter, 3-1 ordering information, 6-1 p package dimensions, 6-2 pin assignment 6-3 pin functions input port, 4-3 output port, 4-4 programming and register descriptions register bit formats, 4-6 programming descriptions, 4-1 programming, 4-1 r r/w, 2-3 ready-to-receive, 3-4 receivers, 3-2 register bit formats, 4-6 register descriptions, 4-1, 4-13 remote-loopback mode, 3-5 reset, 2-3 rs1?s4, 2-4 rxda/rxdb, 2-4 s signals, 2-1 specifications electrical, 5-1 sra, 4-19 srb, 4-20 t timer mode, 3-7 transmitters, 3-1 txda/txdb, 2-4 v vcc, 2-2 |
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