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| MIC74 Micrel MIC74 2-Wire Serial I/O Expander and Fan Controller Advance Information General Description The MIC74 is a fully programmable serial-to-parallel I/O expander compatible with the SMBusTM (system management bus) protocol. It acts as a "slave" on the bus, providing eight independent I/O lines. Each I/O bit can be individually programmed as an input or output. If programmed as an output, each I/O bit can be programmed as an open-drain or complementary push-pull output. If desired, the four most significant I/O bits can be programmed to implement fan speed control. An internal clock generator and state machine eliminate the overhead generally associated with "bit-banging" fan speed control. Programming the device and reading/writing the I/O bits is accomplished using seven internal registers. All registers can be read by the host. Output bits are capable of directly driving high-current loads such as LEDs. A separate interrupt output can notify the host of state changes on the input bits without requiring the MIC74 to perform a transaction on the serial bus or be polled by the host. Three address selection inputs are provided, allowing up to eight devices to share the same bus and provide a total of 64 bits of I/O. The MIC74 is available in an ultra-small-footprint 16-lead QSOP. Low quiescent current, small footprint, and low package height make the MIC74 ideal for portable and desktop applications. Features * Provides eight bits of general purpose I/O * Built in fan speed control logic (optional) * 2-wire SMBusTM/I2CTM compatible serial interface plus interrupt output * 2.7V to 3.6V operating voltage range * 5V-tolerant I/O * Low quiescent current: 2A (typical) * Bit-programmable I/O options: input or output push-pull or open-drain output interrupt on input changes * Outputs can directly drive LEDs (10mA IOL) * Up to 8 devices per bus Applications * * * * * General purpose I/O expansion via serial bus Personal computer system management Distributed sensing and control Microcontroller I/O expansion Fan Control Ordering Information Part Number MIC74BQS Temperature Range -40C to +85C Package 16-lead QSOP Typical Application 3.0V MIC74 R9 ALERT DATA CLK VDD /ALERT DATA CLK A0 A1 A2 GND P0 P1 P2 P3 P4 P5 P6 P7 LED1 R1 R2 R3 R4 R5 R6 R7 R8 3.0V LED8 Serial-Bus-Controlled LED Annunciator SMBusTM is a trademark of Intel Corporation. I2CTM is a trademark of Phillips Electronics N.V. Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com August 1, 2000 1 MIC74 MIC74 Micrel Pin Configuration A0 1 A1 2 A2 3 P0 4 P1 5 P2 6 P3 7 GND 8 16 VDD 15 DATA 14 CLK 13 /ALERT 12 P7 (/FS2) 11 P6 (/FS1) 10 P5 (/FS0) 9 P4 (/SHDN0) 16-Lead QSOP Pin Description Pin Number 1-3 4-7 8 9-12 Pin Name A0-A2 P0-P3 GND P4-P7 (/SHDN, /FS0-/FS2) Pin Function Address (Input): Slave address selection inputs; sets the three least significant bits of the MIC74's slave address. Parallel I/O (Input/Output): General-purpose I/O pin. Direction and output type are user programmable. Ground Parallel I/O (Input/output): P4-P7 are general-purpose I/O pins. Direction and output type are user programmable. Shutdown (Output): When the FAN bit is set, pin 9 becomes SHDN. Fan Speed (Output): When the FAN bit is set, pins 10 through 12 become / FS0-/FS2 respectively, controlled by the FAN_SPEED register. Interrupt (Output): Active-low, open-drain output signals input-changeinterrupts to the host on this pin. Signal is cleared when the bus master (host) polls the ARA (alert response address = 0001 100) or reads status. Serial Bus Clock (Input): The host provides the serial bit clock in this input. Serial Data (Input/Output): Serial data input and open-drain serial data output. Power Supply (Input.) 13 /ALERT 14 15 16 CLK DATA VDD MIC74 2 August 1, 2000 MIC74 Micrel Absolute Maximum Ratings (Note 1) Supply Voltage (VDD) ................................................. +4.6V Input Voltage [all pins except VDD and GND] (VIN) ........................ GND - 0.3V to 5.5V Junction Temperature (TJ) ...................................... +150C Lead Temperature (10 sec.) .................................... +260C ESD Rating, Note 3 VDD ........................................................................................... 1.5kV A0,A1,A2 ................................................................. 500V Others ..................................................................... 200V Operating Ratings (Note 2) Supply Voltage (VDD) .................................. +2.7V to +3.6V Ambient Temperature (TA) ......................... -40C to +85C Package Thermal Resistance ............................... 163C/W Electrical Characteristics 2.7V VDD 3.6V; TA = 25C, bold values indicate -40C TA +85C; unless noted. Symbol VIN IDD ISTART Parameter Input Voltage, any pin except VDD and GND Operating Supply Current Fan Startup Supply Current (Fan Mode Only) Standby Supply Current P[7:0] inputs; P[7:0] = VDD or GND /ALERT open; fCLK = 100kHz during tSTART; /ALERT, /SHDN, /FS2[2:0] = open; VSMBCLK = VSMBDATA = VDD; P[3:0] = inputs /ALERT = open, VSMBCLK = VSMBDATA = VDD; P[3:0] = inputs 1 Condition Min GND-0.3 2 Typ Max 5.5 6 1.75 Units V A mA ISTBY 3 A Serial I/O (DATA, CLK) VIL VIH VOL ILEAK CIN VIL VIH IOL IOH ILEAK CIN COUT VIL VIH ILEAK Input Low Voltage Input High Voltage Output Low Voltage Leakage Current Input Capacitance IOL = 3mA VIN = 5.5V or GND -1 10 -0.3 2.0 0.8 5.5 0.4 +1 V V V A pF Parallel I/O [P0-P3, P4(/SHDN), P5(/FS0)-P7(/FS2)] Input Low Voltage Input High Voltage Output Low Current VOL = 0.4V, VDD = 2.7V VOL = 1V, VDD = 3.3V Output High Current Leakage Current Input Capacitance Output Capacitance VOH = 2.4V VIN = 5.5V or GND -0.5 2 7 10 7 -1 10 10 +1 0.8 5.5 V V mA mA mA A pF pF Address Input (A0-A2) Input Low Voltage Input High Voltage Leakage Current VIN = VDD or GND -0.3 0.7VDD -250 0.3VDD VDD+0.3 +250 V V nA August 1, 2000 3 MIC74 MIC74 Symbol /ALERT VOL ILEAK tSTART tPULSE t/INT t/IR tHD:STA tSU:STA tSU:STO tHD:DAT tSU:DAT tTIMEOUT tLOW tHIGH tF tR tBUF Note 1. Note 2. Note 3. Note 4. Micrel Parameter Condition Min Typ Max Units Output Low Voltage Leakage Current IOL = 1mA VIN = VDD or VSS normal operation minimum pulse-width on Pn to generate an interrupt, Note 7 interrupt delay from state change on Pn to /ALERT VOL, Note 7 -1 250 0.4 +1 V A AC Characteristics Fan Startup Interval Minimum Pulse-Width Interrupt Delay Delay from Status Read or ARA Response to /ALERT VOH Hold Time, Note 7 Setup Time, Note 7 Stop Condition Setup Time Data Hold Time Data Setup Time Clock Low Time-Out Clock Low Period Clock High Period Clock/Data Fall Time Clock/Data Rise Time Bus free time between stop and Start condition hold time after repeated start condition. after this period, the first clock is generated. repeated start condition setup time Note 7 Note 7 Note 7 Notes 4, 7 Notes 5, 7 Notes 5, 7 Notes 6, 7 Notes 6, 7 Note 7 4.7 4.0 4.7 4.0 500 0 25 4.7 4.0 50 300 1000 35 0.5 10 4 4 1 3.3 sec ns s s s s s ns ns ms s s ns ns s Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Devices participating in a transfer will timeout when any clock low exceeds the value of tTIMEOUT(min) of 25ms. Devices that have detected a timeout condition must reset the communication no later than tTIMEOUT(max) of 35ms. The maximum value specified must be adhered to by both a master and a slave as it incorporates the cumulative stretch limit for both a master (10ms) and a slave (25ms). tHIGH(max) provides a simple guaranteed method for devices to detect bus idle conditions. Rise and fall time is defined as follows: tR = VIL(max) - 0.15V to VIH(min) + 0.15V; tF = 0.9VDD to VIL(max) - 0.15V. Guaranteed by design. Note 5. Note 6. Note 7. Timing Definitions tR CLK tLOW tHD:STA tBUF DATA StoP Start Start StoP tHD:DAT tSU:DAT tHD:STA tHIGH tSU:STA tSU:STO tF MIC74 4 August 1, 2000 MIC74 Micrel Register Descriptions Device Configuration Register DEV_CFG D[7] D[6] D[5] D[4] D[3] D[2] D[1] FAN D[0] IE D[7] D[6] D[5] Always write as zero. Output Configuration Register OUT_CFG D[4] D[3] D[2] D[1] D[0] OUT7 OUT6 OUT5 OUT4 OUT3 OUT2 OUT1 OUT0 Power-On Default Value: 0000 0000b, 00h Interrupts disabled Not in Fan Mode Command_byte addess: 0000 0000b, 00h Type: 8-bits, read/write Bit Name: IE Function: Global interrupt enable. Operation: 1 = enabled 0 = disabled FAN Selects Fan Mode (P[7:4] vs. /FS[2:0], /SHDN) Operation: 1 = Fan Mode 0 = I/O Mode Bit Name: D[2] through D[6] Function: Reserved Operation: Reserved--always write as zero Data Direction Register DIR D[7] DIR7 D[6] DIR6 D[5] DIR5 D[4] DIR4 D[3] DIR3 D[2] DIR2 D[1] DIR1 D[0] DIR0 Power-On Default Value: 0000 0000b, 00h all outputs open-drain Command_byte addess: 0000 0010b, 02h Type: 8-bits, read/write Bit Name: Function: OUTn Selects output driver configuration of Pn when Pn is configured as an output. Operation: 1 = push-pull 0 = open-drain Notes: If Fan Mode is selected, that is, the FAN bit of the DEV_CFG register is set to one, P[7:4] are automatically configured as open-drain outputs. They are then referred to as /FS[2:0] and /SHDN. The OUT_CFG register has no effect on these I/O bits while in Fan Mode. Bit Name: Function: Status Register STATUS D[7] S7 D[6] S6 D[5] S5 D[4] S4 D[3] S3 D[2] S2 D[1] S1 D[0] S0 Power-On Default Value: 0000 0000b, 00h all Pn's configured as inputs Command_byte addess: 0000 0001b, 01h Type: 8-bits, read/write Bit Name: DIRn Function: Selects data direction, input or output, of Pn Operation: 1 = output 0 = input Notes: If Fan Mode is selected, that is, the FAN bit of the DEV_CFG register is set to one, P[7:4] are automatically configured as open-drain outputs. They are then referred to as /FS[2:0] and /SHDN. The DIR register has no effect on these I/O bits while in Fan Mode. Power-On Default Value: 0000 0000b, 00h no interrupts pending Command_byte addess: 0000 0011b, 03h Type: 8-bits, read only Sn Flag for Pn input-change event when Pn is configured as an input; Sn is set when the corresponding input changes state. Operation: 1 = change occured 0 = no change occured Notes: If Fan Mode is selected, that is, the FAN bit of the DEV_CFG register is set to one, P[7:4] are automatically configured as open-drain outputs. They are then referred to as /FS[2:0] and /SHDN. No interrupts of any kind are generated by these pins while in Fan Mode. All status bits are cleared after any read operation is performed on STATUS. 5 MIC74 Bit Name: Function: August 1, 2000 MIC74 Micrel Interrupt Mask Register INT_MASK D[7] IM7 D[6] IM6 D[5] IM5 D[4] IM4 D[3] IM3 D[2] IM2 D[1] IM1 D[0] IM0 Fan Speed Register FAN_SPEED D[7] D[6] D[5] D[4] D[3] D[2] D[1] Fan Speed D[0] Always write as zero. Power-On Default Value: 0000 0000b, 00h Command_byte addess: 0000 0100b, 04h Type: 8-bits, read/write IMn Interrupt enable bit for Pn when Pn is configured as an input Operation: 1 = enabled 0 = disabled Notes: If Fan Mode is selected, that is, the FAN bit of the DEV_CFG register is set to one, P[7:4] are automatically configured as open-drain outputs. They are then referred to as /FS[2:0] and /SHDN. No interrupts of any kind are generated by these pins while in Fan Mode. Bit Name: Function: Power-On Default Value: 0000 0000b, 00h fan off Command_byte addess: 0000 0110b, 06h Type: 8-bits, read/write Bit Name: D[0] through D[2] Function: Determines bit-pattern on FS[2:0] Operation: D[2:0] Value 000 001 010 011 100 101 110 111 Output State /FS[2:0] 111 110 101 100 011 010 001 000 /SHDN 0 1 1 1 1 1 1 1 Fan Speed off speed 1 (slowest) speed 2 speed 3 speed 4 speed 5 speed 6 speed 7 (fastest) Data Register DATA D[7] P7 D[6] P6 D[5] P5 D[4] P4 D[3] P3 D[2] P2 D[1] P1 D[0] P0 Fan Speed Settings Notes: Any time the fan speed register contains zero, that is, the fan is shut down, and a non-zero value is written into the fan speed register, the /FS[2:0] and /SHDN outputs will assume the highest fan speed state for approximately one second (tSTART). Following this interval, the state of the fan speed control outputs will assume the value indicated by the contents of FAN_SPEED. This insures that the fan will start reliably when low speed operation is desired. Power-On Default Value: 1111 1111b, FFh Command_byte addess: 0000 0101b, 05h Type: 8-bits, read/write Bit Name: Function: Pn Returns the current state of any Pn configured as an input and the last value written to Pn's configured as outputs; Writing the DATA register sets the output state of any Pn's configured as outputs; writes to I/O bits configured as inputs are ignored. Read Operation: 1 = Pn is high 0 = Pn is low Write Operation: 1 = Pn is set to one 0 = Pn is cleared Notes: If Fan Mode is selected, that is, the FAN bit of the DEV_CFG register is set to one, P[7:4] are automatically configured as open-drain outputs. They are then referred to as /FS[2:0] and /SHDN. The state of these pins is determined by the FAN_SPEED register. While in Fan Mode, D[7:4] of the DATA registers have no effect. 6 Bit Name: D[3] through D[7] Function: Reserved Operation: Always write as zero. MIC74 August 1, 2000 MIC74 Micrel Functional Diagram INTn IMn STATUSn Q S EDGE DETECT QR STATUS_READn DATAn (INPUT) OUT_CFGn VDD Pn (typical I/O port) DIRn DATAn (OUTPUT) GND Typical I/O Port (Fan Speed Control Logic Not Shown) Functional Description Pin Descriptions VDD Power supply input connection. See "Operating Ratings." GND Ground or return connection for all MIC74 functions. CLK An CLK signal is provided by the host (master) and is common to all devices on the bus. The CLK signal controls all transactions in both directions on the bus and is applied to each MIC74 at the CLK pin. DATA Serial data is bidirectional and is common to all devices on the bus. The MIC74's DATA output is open-drain. The DATA line requires one external pull-up resistor or current source per system that can be located anywhere along the line. A2, A1, A0 An MIC74 responds to its own unique address which is assigned using the A0-A2 pins. A0-A2 set the three LSBs (least significant bits) of the MIC74's 7-bit slave address. The three address pins allow eight unique MIC74 addresses in a system. When the MIC74's address matches an address received in the serial bit stream, communication is initiated. A2, A1 and A0 should be connected to GND or VDD. The state of these pins is sampled only once at device power-on. New slave addresses are not accepted unless the MIC74 is powered off then on. A2 0 0 0 0 1 1 1 1 Inputs A1 0 0 1 1 0 0 1 1 A0 0 1 0 1 0 1 0 1 MIC74 Slave Address Binary 010 0000b 010 0001b 010 0010b 010 0011b 010 0100b 010 0101b 010 0110b 010 0111b Hex 20h 21h 22h 23h 24h 25h 26h 27h Table 1. MIC74 Address Configuration Alert Response Address The MIC74 also responds to the ARA (Alert Response Address). The ARA is used by the master (host) to request the address of a slave that has provided an interrupt to the master via the /ALERT line. The ARA is a single address (0001 100) common to all slaves and is described in more detail under "Interrupt Generation" with related information under "/ALERT." Also see Figure 7. Pn, /SHDN, and /FS0-/FS2 P0 through P7 are general-purpose input/output bits. Each bit is independently programmable as an input or an output. If programmed as an output, each bit is further programmable as either a complementary push-pull or open-drain output. If properly enabled, any Pn programmed as an input will generate an interrupt to the host using the /ALERT output when the input changes state. In this way, the MIC74 can August 1, 2000 7 MIC74 MIC74 notify the host of an input change without requiring periodic polling by the host or a message transaction on the bus. Regardless of whether interrupts are enabled or disabled, each input-change event also sets the corresponding bit in the status register. I/O configuration is performed using the output configuration (OUT_CFG), I/O direction (DIR), and interrupt mask (INT_MASK) registers. If the FAN bit in the device configuration register is set, the states of P[7:4] are controlled by the FAN_SPEED register. The bits in the OUT_CFG, DIR, and INT_MASK registers corresponding to P[7:4] are ignored. When in Fan Mode, P[7:4] are referred to as /FS2, /FS1, /FS0, and /SHDN. While in this mode, no interrupts of any kind will be generated by these pins. Micrel the MIC74, the command byte is the address of the target register. See Table 2. In addition, to the read byte and write byte protocols, the MIC74 adheres to the SMBus protocol for response to the ARA (alert response address). An MIC74 expects to be interrogated using the ARA when it has asserted its /ALERT output. /ALERT interrupts can be enabled or disabled using the IE bit in the DEV_CFG register. Power-On When power is initially applied, the MIC74's internal registers will assume their power-up default state and the state of the address inputs, A2, A1 and A0, will be read to establish the device's slave address. See the individual register descriptions for each registers default state. Also see Table 2. I/O Ports Each I/O bit, P0 through P7, may be individually programmed as an input or output using the corresponding bit in the I/O direction register, DIR. If programmed as an output, each is further programmable as either a complementary push-pull or open-drain output using the output configuration register, OUT_CFG. If enabled by the corresponding bit, IMn, in the interrupt mask register INT_MASK, each Pn programmed as an input will generate an interrupt to the host on /ALERT if the input changes state. In this way, the MIC74 can notify the host of an input change without requiring periodic polling by the host or a transaction on the bus. Each input-change event also sets the corresponding bit in the status register, STATUS. See "Functional Diagram" for the logic arrangement of a typical MIC74 I/O port. Fan Speed Control If the FAN bit in the device configuration register is set, the state of P[7:4] is controlled by the FAN_SPEED register. The bits in the OUT_CFG, DIR, and INT_MASK registers corresponding to P[7:4] are ignored. When in Fan Control Mode, P[7:4] are referred to as /FS2, /FS1, /FS0, and /SHDN. While in this mode, no interrupts of any kind will be generated by these pins. See "Applications Information" for typical fan speed control applications. /ALERT The alert signal is an open-drain, active-low output. The operation of the /ALERT output is controlled by the IMn bits in the INT_MASK register and the global interrupt enable bit (IE) in the DEV_CFG register. If the IE bit is set to zero, or if the corresponding interrupt enable bit, IMn, is set to zero, no input-change interrupts will be generated. (Regardless of the IE bit setting, the change will be reflected in the status register.) If the IE bit is set to one, IMn is set to one, and Pn is an input, then /ALERT is driven active whenever Pn changes state, (goes from a high-to-low or low-to-high state). Once triggered, /ALERT is unconditionaly reset to its inactive state once the MIC74 successfully responds to the alert response address or STATUS is read. Serial Port Operation The MIC74 uses standard SMBus Read_Byte and Write_Byte operations to communicate with its host. The Read_Byte operation is a composite read-write operation consisting of first sending the MIC74's slave address followed by a command byte (a write) and then resending the slave address and clocking out the data byte (a read). The command byte is the address of the target register. See Table 2. An example of a Read_Byte operation is shown in Figure 8. Similarly, the write-byte operation consists of sending the device's slave address followed by a command byte and the byte to be written to the target register. Again, in the case of Register Name DEV_CONFIG DIR OUT_CFG STATUS INT_MASK DATA FAN_SPEED Register Description Device Configuration I/O Direction Output Configuration Interrupt Status Interrupt Mask General-Purpose I/O Fan Speed Address Binary 0000 0000b 0000 0001b 0000 0010b 0000 0011b 0000 0100b 0000 0101b 0000 0110b Hex 00h 01h 02h 03h 04h 05h 06h Available Operations 8-bit read/write 8-bit read/write 8-bit read/write 8-bit read 8-bit read/write 8-bit read/write 8-bit read/write Power-On Default Binary 0000 0000b 0000 0000b 0000 0000b 0000 0000b 0000 0000b 1111 1111b 0000 0000b Hex 00h 00h 00h 00h 00h FFh 00h Table 2. Register Summary MIC74 8 August 1, 2000 MIC74 Fan Start-Up Any time the fan speed register contains zero (fan is off) and then a nonzero value is written to FAN_SPEED, the /FS[2:0] and /SHDN outputs will assume the highest fan speed state for approximately one second (tSTART). Following this interval, the state of the fan speed control outputs will assume the value indicated by the contents of FAN_SPEED. This insures that the fan will start reliably when low speed operation is desired. The tSTART interval is generated by an internal oscillator and counters. At the end of tSTART, this oscillator is powered down to reduce overall power consumption. Regulator VIN VOUT /SHDN FB GND Micrel state first, then, after a delay equal to one-half of tSTART, the /SHDN pin is deasserted. Conversely, when the fan is shut down (zero is written to FAN_SPEED), the /SHDN pin is deasserted first. The /FS[2:0] lines are subsequently deasserted after a delay of 12 tSTART. The internal oscillator is also powered down following the tSTART/2 interval at fan shutdown. These timing relationships are illustrated in Figure 2. Interrupt Generation Assuming that any or all of the I/O's are configured as inputs, the MIC74 will reflect the occurrence of an input change in the corresponding bit in the status register, STATUS. This action cannot be masked. An input change will only generate an interrupt to the host if interrupts are properly configured and enabled. The MIC74 can operate in either polled mode or interrupt mode. In the case of polled operation, the host periodically reads the contents of STATUS to determine the device state. The act of reading STATUS clears its contents. Repeating events which have occurred since the last read from STATUS will not be discernable to the host. Interrupts are only generated if the global interrupt enable bit, IE, in the DEV_CFG register is set. The /ALERT signal will be asserted (driven low) when an interrupt is generated. The MIC74 expects to be interrogated using the ARA when it has generated an interrupt output. Once it has successfully responded to the ARA (Alert Response Address), the /ALERT output will be deasserted. The contents of the status register will not be cleared until it is read using a read byte operation. If a given system does not wish to use the SMBus ARA protocol for reporting interrupts, the system may simply poll the contents of the status register after detecting an interrupt on /ALERT. This action will clear the contents of STATUS and cause /ALERT to be deasserted. Reading the status register is an acceptable substitute for using the ARA protocol. Presumably, however, it will involve higher system overhead since all the devices on the bus must be polled to determine which one generated the interrupt. RPULL-UP RFB FAN /SHDN /FS2 RF2 /FS1 RF2 /FS0 RF2 RMIN_SPEED MIC74 Figure 1. Fan Speed Control Application Proper sequencing of the /FS[2:0] and /SHDN signals is performed by the MIC74's internal logic state machine. When activating the fan from the off state, the /FS[2:0] lines change Fan Supply Output Voltage* Fan Rotation Speed* shutdown Value written to FAN_SPEED (00h) /FS2 tSTART 01h 01h 02h 07h 05h shutdown 00h * FAN SUPPLY OUTPUT VOLTAGE AND SPEED ARE NOT TO SCALE. /FS1 tSTART/2 /FS0 tSTART/2 /SHDN Figure 2. Typical MIC74 Fan-Mode Timing and System Behavior August 1, 2000 9 MIC74 MIC74 Micrel DATA Applications Information Bit Transfer The data received on the DATA pin must be stable during the high period of the clock. DATA Data Stable, Data Valid Data Change Allowed CLK Start StoP Figure 4. Start and Stop Definitions Start (S) and stop (P) conditions are always generated by the bus master (host). After a start condition, the bus is considered to be busy. The bus becomes free again after a certain time following a stop condition or after both CLK and DATA lines remain high for more than 50s. Serial Byte Format Every byte consists of 8 bits. Each byte transferred on the bus must be followed by an acknowledge bit. Bytes are transferred with the MSB (most significant bit) first. See Figure 5. CLK Figure 3. Acceptable Bit Transfer Conditions Data can change state only when the CLK line is low. Refer to Figure 3. Start and Stop Conditions Two unique bus situations define "start" and "stop" conditions. A high-to-low transition of the DATA line while CLK is high indicates a start condition. A low-to-high transition of the DATA line while CLK is high defines a stop condition. See Figure 4. MSB DATA 1 2 3 4 5 6 7 8 9 LSB 1 2 3 4 5 6 7 8 9 CLK ACK ACK Start Byte Complete StoP Figure 5. Serial Byte Format Acknowledge and Not Acknowlege The acknowledge related clock pulse is generated by the master. The transmitter releases the DATA line (high) during the acknowledge clock cycle. In order to acknowledge (ACK) a byte, the receiver must pull the DATA line low during the high period of the clock pulse according the bus timing specifications. A slave device that wishes to not acknowledge a byte must let the DATA line remain high during the acknowledge clock pulse. See Figure 6. MSB DATA (Host) DATA (Slave MIC74) 1 2 3 4 5 6 7 LSB NAK (high) 8 9 ACK (low) CLK ACK Figure 6. Acknowledge and Not Acknowledge MIC74 10 August 1, 2000 MIC74 Micrel Master-to-slave transmission Slave-to-master response R/W = READ NOT ACKNOWLEDGE ACKNOWLEDGE STOP S 0 0 0 1 1 0 0 1 A 0 1 0 0 A2 A1 A0 0 /A P Alert Response Address (master requests address of interupting device) P0* t/INT /ALERT * Assumes P0 interrupts properly configured and enabled. P0 used as an example. Timing for P1 to P7 is identical. t/IR Slave Address (interrupting MIC74 announces its address) Figure 7. Interrupt Handling Using the Alert Response Address Master-to-slave transmission Slave-to-master response R/W = WRITE ACKNOWLEDGE ACKNOWLEDGE R/W = READ NOT ACKNOWLEDGE ACKNOWLEDGE STOP S 0 0 0 1 A2 A1 A0 0 A 0 0 0 0 0 0 1 1 A S 0 0 0 1 A2 A1 A0 1 A X X X X X X X X /A P Slave Address (host addresses an MIC74) Command Byte (03h = selects status register) Slave Address (host addresses an MIC74) Status Value (MIC74 sends status) P0* t/INT /ALERT * Assumes P0 interrupts properly configured and enabled. P0 used as an example. Timing for P1 to P7 is identical. STATUS t/R register is cleared to zero following this operation. Figure 8. Interrupt Handling Without the Alert Response Address August 1, 2000 11 MIC74 MIC74 Initializing the MIC74 The MIC74's internal registers are reset to their default state at power-on. The MIC74's default state can be summarized as follows: * All I/O's configured as inputs (DIR = 00h) * Output configuration set to open-drain (OUT_CFG = 00h) * All outputs high/floating (DATA = FFh) * Fan functions disabled (FAN_SPEED = 00h, FAN bit of DEV_CFG = 0) * All interrupts masked (IE bit of DEV_CFG = 0) The result of this configuration is that all I/O pins will essentially float unless driven by external circuitry. Any system using the MIC74 will need to initialize the internal registers to the state required for proper system operation. The recommended order for initializing the MIC74's registers is as follows: Micrel 1. Write DATA 2. Write OUT_CFG 3. Write DIR 4. Write FAN_SPEED (if using fan mode) 5. Write INT_MASK (if using interrupts) 6. Read STATUS to clear it. 7. Write DEV_CFG to enable fan mode and/or interrupts, if using At the conclusion of step three, any I/O's configured as outputs in step two will be driven to the levels programmed into the data register in step one. The order of step 1 through step 3 is important to insure that spurious data does not appear at the I/O's during configuration. Following step 7, programming the device configuration register, the MIC74 will begin generating interrupts if they are enabled, and the fan will be started if FAN_SPEED contains a nonzero value. The corresponding interrupt service routines (if any) must be initialized and enabled prior to step seven. STATUS should be cleared (step 6) in both polled and interrupt driven systems. Initialize for interrupts Initialize for polling Write desired ouput values to DATA Write desired output values to DATA Set output configuration in OUT_CFG Set output configuration in OUT_CFG Set desired I/O's as outputs by writing DIR Set desired I/O's as outputs by writing DIR Set initial fan speed in FAN_SPEED (if using) Set initial fan speed in FAN_SPEED (if using) Write INT_MASK to enable interrupts (if using) Write DEV_CFG to turn on fan (if using) Read STATUS to clear it Read STATUS to clear it Write DEV_CFG to turn on interrupts and fan (if using) Initialization complete Initialization complete Figure 9a. Initializing the MIC74 for Polled Operation Figure9b. Initializing the MIC74 for Interrupts MIC74 12 August 1, 2000 MIC74 Polled Mode Input state changes on I/O's configured as inputs will be reflected in the status register regardless of the state of the global interrupt enable bit (IE) and the individual interrupt mask bits in INT_MASK. In a system utilizing polling to monitor for input changes, the status register is periodically read to check for input events. The act of reading STATUS clears it in preparation for detecting future events. The status bits corresponding to I/O's configured as outputs or corresponding to P[7:4] when in fan mode will not be set by state changes on these pins. It is always good practice, however, to mask the value obtained when reading STATUS to eliminate any bits, output or otherwise, that are not of immediate concern. This will help avoid problems if software changes are made in the future. The flowchart shown in Figure 9a illustrates the steps involved in initializing the MIC74 for polled operation. The flowchart in Figure 10 illustrates the corresponding polling routine. The process for writing output data is straightforward--simply write the desired bit pattern to DATA. (Special precautions may be required when changing output data in an interrupt driven system, however. See the discussion below under "Writing to the Data Register.") Micrel Interrupt Mode Input state changes on I/Os configured as inputs will be reflected in the status register regardless of the state of the global interrupt enable bit (IE) and the individual interrupt mask bits in INT_MASK. In a system utilizing interrupts to detect input changes, one or more of the bits in the interrupt mask register, INT_MASK, are set to allow interrupts on /ALERT to be generated by input events. The global interrupt enable bit, IE, in the device configuration register must also be set to enable interrupts. The flowchart shown in Figure 9b illustrates the steps involved in initializing the MIC74 for interrupt-driven operation. The flowchart in Figure 11 illustrates the corresponding interrupt service routine using the SMBus ARA (alert response address). The corresponding timing diagram is shown in Figure 7. The flowchart in Figure 12 illustrates the corresponding interrupt service routine using polling to determine the interrupt source. Figure 8 illustrates the timing. Utilizing the ARA greatly speeds identification of the interrupting slave device and lowers latency, as only a single transaction on the bus is necessary to identify the interrupt source. Using either method, STATUS must be read to determine the exact source of the interrupt within the MIC74. The act of Polling the MIC74 Read STATUS Is No STATUS 00h ? Yes Is Sn set ? No Yes Service function n Is Sm set ? No Yes Service function m Is Sx set ? No Yes Service function x Figure 10: Polling the MIC74 August 1, 2000 13 MIC74 MIC74 reading STATUS clears it in preparation for detecting future events. The status bits corresponding to I/O's configured as outputs or corresponding to P[7:4] when in fan mode will not be set by state changes on these pins. It is always good practice, however, for the interrupt service routine to mask the value obtained when reading STATUS to eliminate any bits, output or otherwise, that are not of immediate concern. This will help avoid problems if software changes are made in the future. The process for writing output data is straightforward-- simply write the desired bit pattern to DATA. Special precautions may be required, however, when changing output data in an interrupt driven system. See the discussion below under "Writing to the Data Register." Micrel Writing To The Data Register Multiple software routines may use the various output bits available on the MIC74 to control individual functions such as power switches, LED's, etc. These various functions may be handled by independent software routines which must manipulate individual output bits without regard for other bits. Care must be taken to insure that these various software routines do not interfere with each other when modifying output data. The recommended procedure for changing isolated output bits is as follows: 1. Read DATA 2. Set desired bits by ORing the value read from DATA with an appropriate mask value 3. Clear desired bits by ANDing the value read from DATA with an appropriate mask value 4. Write the result back to DATA A functionally equivalent alternative to this procedure is to keep an image of the data register in software. Any independent routines would make changes to this image using the procedure above and then call a routine that actually writes Interrupt Service Routine Read alert response address Is interrupt from MIC74 Yes No Service other devices Polled I.S.R. Read STATUS to determine source Read STATUS Is Sn set ? No Yes Service function n Is No STATUS 00h ? Yes Service other devices Is Sm set ? No Yes Service function m Is Sn set ? No Yes Service function n Is Sx set ? No Yes Service function x Is Sm set ? No Yes Service function m Yes Interrupts pending ? No Is Sx set ? No Yes Service function x Return from ISR Return from ISR Figure 11: Interrupt Service Routine Using the ARA Figure 12: Interrupt Service Routine Without ARA MIC74 14 August 1, 2000 MIC74 the new image to DATA. Interrupts would be disabled briefly while DATA is being modified. Regardless of which procedure is used, it is important that only one software routine at a time attempts to make changes to the output data. In a system where polling is the exclusive method for servicing inputs, this is usually not a problem. If interrupts are employed to any degree in dealing with MIC74 inputs, care must be taken to insure that a software routine in the midst of making changes to outputs is not interrupted by another routine that proceeds to make its own changes. The risk is that the value in DATA will be changed by an interrupting routine after it is read by a different routine in the process of making its own changes. If this occurs, the value written to DATA by the first routine may be incorrect. The most straightforward solution to this potential problem is to disable system interrupts while the data register is actually being modified. Application Circuits The MIC74, in conjunction with a linear low-dropout or switching regulator, can be configured as a fan speed controller. Most adjustable regulators have a feedback pin and use an external resistor divider to adjust the output voltage. The MIC74 is designed to take advantage of this configuration with its ability to manipulate multiple feedback resistors connected to the P4-P7 outputs. Individual open-drain output bits are selectively grounded or allowed to float under the control of the internal state machine. This action raises or Micrel lowers the equivalent resistance seen in the regulator's feedback path, thus changing the output voltage. Any conventional adjustable regulator is usually suitable for use with the MIC74. The output voltage corresponding to each value to be programmed into the fan speed register can be determined by selecting the resistors in the circuit. The regulator itself can be chosen to meet the needs of the application, such as input voltage, output voltage, current handling capability, maximum power dissipation, and physical space constraints. Two circuit examples are shown below. The circuit of Figure 13 illustrates use of a typical LDO linear regulator such as the MIC29152. A switching regulatorbased fan control circuit using the MIC4574 200kHz Simple 0.5A Buck Regulator is shown in Figure 14. Both circuits assume a 12V fan power supply but will accommodate much higher input voltages if required (MIC4574: 24V, MIC29152: 26V). Care must be taken, however, to insure that the maximum power dissipation of the regulator is not exceeded. If the regulator overheats, its internal thermal shutdown circuitry will deactivate it. (See MIC29152 or MIC4574 datasheet.) Since the MIC74 powers up with all its I/O's inputs (floating), both circuits will power-up with the fan running at a minimum speed determined by the value of RMIN_SPEED. Once the MIC74's fan mode is activated by setting the appropriate bit MIC29152 IN OUT EN FB GND +12V +3.3V C1 10F MIC74 VDD /SHDN SMBCLK /FS2 SMBus Host C4 0.1F SMBDATA /FS1 SMBALERT /FS0 A2 P3 A1 P2 A0 P1 GND P0 RF0 RPU 100k RFB 3k C3 220F FAN A-Speed HP2A-B3 or similar RF2 RF1 1.8k RMIN_SPEED 1k 3.5k 1k Figure 13. Fan Speed Control Using an Adjustable Low-Dropout Regulator +3.3V RPU 200k RBASE 150k +3.3V MIC74 VDD /SHDN /FS2 SMBCLK /FS1 SMBDATA SMBALERT /FS0 C4 0.1F A2 A1 A0 GND P3 P2 P1 P0 +12V 2N3906 Q1 100k C1 10F MIC4574 IN SW SHDN FB SGND PGND L1 100H C2 3300pF D1 RFB 3k C3 220F FAN A-Speed HP2A-B3 or similar RF2 RF1 1.8k 1k RF0 3.5k RMIN_SPEED 1k SMBus Host Figure 14. Fan Speed Control Using a Buck Converter August 1, 2000 15 MIC74 MIC74 in the configuration register, the fan will be shutdown by the assertion of the /SHDN output if FAN_SPEED is zero. If FAN_SPEED is programmed with any nonzero value, the fan will be driven to its maximum speed for the duration of tSTART (about 1 second) and then assume the programmed speed. Note that the circuit in Figure 14 contains an additional transistor, Q1, as an inverter because the regulator in this example has an active-high shutdown input rather than an enable input. Otherwise the circuits function identically. Table 3 lists the output voltages corresponding to all the fan speeds and system states possible with these circuits. The following equations are used to calculate the resistor values used in MIC74 fan speed control circuits. It is assumed here that the regulator's internal reference voltage is 1.24V. If the regulator uses a different reference voltage, that value should be used instead. Micrel The following equations show how to calculate the resistor values for the fan controllers. For example, when the fan speed register contains 011b, which is the 3rd lowest speed, RF1 and RF0 are parallel to RMIN to give the equivalence resistor (REQ) value of 545. REQ = RF1 || RF0 || RMIN REQ = 1.8k || 3.6k || 1k REQ = 545 The output voltage is calculated by using: R VOUT = 1.24V 1 + FB REQ 3k VOUT = 1.24V 1 + 545 VOUT = 8.06V FAN_SPEED Value 0000 0000b 0000 0000b 0000 0001b 0000 0010b 0000 0011b 0000 0100b 0000 0101b 0000 0110b 0000 0111b Fan Speed Selected power-up fan off lowest 2nd lowest 3rd lowest medium 3rd highest 2nd highest highest RFB 3k 3k 3k 3k 3k 3k 3k 3k 3k RMIN 1k 1k 1k 1k 1k 1k 1k 1k 1k RF2 open open open open open 1k 1k 1k 1k RF1 open open open 1.8k 1.8k open open 1.8k 1.8k RF0 open open 3.6k open 3.6k open 3.6k open 3.6k REQ 1k 1k 783 643 545 500 439 391 353 VOUT 4.96V 0V 5.99V 7.03V 8.06V 8.68V 9.71V 10.75V 11.78V Table 3. Fan Speed Selection MIC74 16 August 1, 2000 MIC74 Micrel Package Information PIN 1 0.157 (3.99) 0.150 (3.81) DIMENSIONS: INCHES (MM) 0.009 (0.2286) REF 0.025 (0.635) BSC 0.0098 (0.249) 0.0040 (0.102) 0.012 (0.30) 0.008 (0.20) 0.0098 (0.249) 0.0075 (0.190) 45 8 0 SEATING 0.0688 (1.748) PLANE 0.0532 (1.351) 0.196 (4.98) 0.189 (4.80) 0.050 (1.27) 0.016 (0.40) 0.2284 (5.801) 0.2240 (5.690) 16-Pin QSOP (QS) August 1, 2000 17 MIC74 MIC74 Micrel MIC74 18 August 1, 2000 MIC74 Micrel August 1, 2000 19 MIC74 MIC74 Micrel MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 2000 Micrel Incorporated MIC74 20 August 1, 2000 |
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