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1 of 19 101207 features ? unique 1-wire ? interface requires only one port pin for communication ? derives power from data line (?parasite power?)?does not need a local power supply ? multi-drop capability simplifies distributed temperature sensing applications ? requires no external components ? 0.5 c accuracy from ?10c to +85c ? measures temperatures from ?55c to +100c (?67f to +212f) ? thermometer resolution is user-selectable from 9 to 12 bits ? converts temperature to 12-bit digital word in 750 ms (max.) ? user?definable non-volatile temperature alarm settings ? alarm search command identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition) ? software compatible with the ds1822-par ? ideal for use in remote sensing applications (e.g., temperature probes) that do not have a local power source pin assignment pin description gnd - ground dq - data in/out nc - no connect description the ds18b20-par digital thermomete r provides 9 to 12?bit centigrade temperature measurements and has an alarm function with nonvol atile user-programmable upper an d lower trigger points. the ds18b20-par does not need an external power supply be cause it derives power directly from the data line (?parasite power?). the ds18b20-par comm unicates over a 1-wire bus, which by definition requires only one data line (and ground) for communicat ion with a central micropr ocessor. it has an operating temperature range of ?55c to +100c and is accurate to 0.5 c over a range of ?10c to +85c. each ds18b20-par has a unique 64-bit identificati on code, which allows multiple ds18b20-pars to function on the same 1?wir e bus; thus, it is simple to use on e microprocessor to control many ds18b20- pars distributed over a large area . applications that can benef it from this feature include hvac environmental controls, temperature monitoring syst ems inside buildings, equipment or machinery, and process monitoring and control systems. ds18b20-par 1-wire parasite-powe r digital thermomete r www.maxim - ic.com to-92 ( ds18b20-par ) 1 ( bottom view ) 2 3 dallas 18b20p 1 gnd dq nc 2 3 1-wire is a registered trademark of dallas semiconductor.
ds18b20-par 2 of 19 detailed pin descriptions table 1 pin symbol description 1 gnd ground. 2 dq data input/output pin. open-drain 1-wire interfa ce pin. also provides power to the device when used in parasite po wer mode (see ?parasite power? section.) 3 nc no connect. doesn?t connect to internal circuit. overview the ds18b20-par uses dallas? exclusive 1-wire bus protocol that implements bus communication using one control signal. the control line requires a weak pullup resistor since all devices are linked to the bus via a 3-state or open-drain port (the dq pin in the case of the ds18b20-par). in this bus system, the microprocessor (the master device) iden tifies and addresses devices on the bus using each device?s unique 64-bit code. becau se each device has a unique code, the number of devices that can be addressed on one bus is virtually unlimited. the 1- wire bus protocol, including detailed explanations of the commands and ?time slots,? is covered in the 1-wire bus system secti on of this datasheet. an important feature of the ds18b20-par is its abil ity to operate without an external power supply. power is instead supplied through the 1-wire pullup re sistor via the dq pin when the bus is high. the high bus signal also charges an internal capacitor (c pp ), which then supplies power to the device when the bus is low. this method of deriving power from th e 1-wire bus is referred to as ?parasite power.? figure 1 shows a block diagram of the ds18b20-par, and pin descriptions are given in table 1. the 64-bit rom stores the device?s uni que serial code. the scratchpad memory contains the 2-byte temperature register that stores th e digital output from the temperature sensor. in addition, the scratchpad provides access to the 1-byte upper a nd lower alarm trigger registers (t h and t l ). the t h and t l registers are nonvolatile (eeprom), so they will retain their data when the device is powered down. ds18b20-par block diagram figure 1 c pp v pu 4.7k 64-bit rom and 1-wire port d q internal v dd parasite power circuit memory control logic scratchpad 8-bit crc generator temperature sensor alarm high trigger (t h ) register (eeprom) alarm low trigger (t l ) register (eeprom) configuration register (eeprom) gnd ds18b20-par
ds18b20-par 3 of 19 parasite power the ds18b20-par?s parasite power circuit allows the ds18b20-par to operate without a local external power supply. this ability is especially useful for a pplications that require remo te temperature sensing or that are very space constrained. figure 1 shows the ds18b20-par?s parasite-power control circuitry, which ?steals? power from the 1-wire bus via the dq pin when the bus is high. the stolen charge powers the ds18b20-par while the bus is high, and some of the charge is stored on the parasite power capacitor (c pp ) to provide power when the bus is low. the 1-wire bus and c pp can provide sufficient parasite power to the ds18b20-par for most operations as long as the specified timing and voltage requi rements are met (refer to the dc electrical characteristics and the ac elec trical characteristics sectio ns of this data sheet). however, when the ds18b20-par is performing temp erature conversions or copying data from the scratchpad memory to eeprom, the operating current can be as high as 1.5 ma. this current can cause an unacceptable voltage drop across the weak 1-wire pu llup resistor and is more current than can be supplied by c pp . to assure that the ds18b20-par has su fficient supply current, it is necessary to provide a strong pullup on the 1-wire bus whenever te mperature conversions are taking place or data is being copied from the scratchpad to eeprom. this can be accomplished by using a mosfet to pull the bus directly to the rail as shown in figure 2. the 1-wire bus must be switched to the strong pullup within 10 s (max) after a convert t [44h] or copy scra tchpad [48h] command is issued, and the bus must be held high by the pullup for the duration of the conversion (t conv ) or data transfer (t wr = 10 ms). no other activity can take place on the 1- wire bus while the pullup is enabled. supplying the ds18b20-par during temperature conversions figure 2 operation ? measuring temperature the core functionality of the ds18b 20-par is its direct-to-digital temp erature sensor. the resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, which corresponds to increments of 0.5 c, 0.25 c, 0.125 c, and 0.0625 c, respectively. the default reso lution at power-up is 12-bit. the ds18b20-par powers-up in a low-pow er idle state; to initiate a temperature measurement and a-to- d conversion, the master must issue a convert t [44h] command. following the conversion, the resulting thermal data is stored in the 2-byte temp erature register in the scratchpad memory and the ds18b20-par returns to its idle state. the ds18b20-par output data is calibrated in degrees centigrade; for fahrenheit applications, a lookup ta ble or conversion routine must be used. the temperature data is stored as a 16- bit sign-extended two?s complement number in the temperature register (see figure 3). the sign bits (s) indicate if the temperature is positiv e or negative: for positive numbers s = 0 and for negative numbers s = 1. if the ds18b20-par is configured for 12-bit resolution, all bits in the temperature register will contain valid data. for 11-bit resolution, bit 0 is undefined. for 10-bit v pu v pu 4.7k 1-wire bus micro- processor ds18b20-pa r gnd dq to other 1-wire devices
ds18b20-par 4 of 19 resolution, bits 1 and 0 are undefined, and for 9-bit re solution bits 2, 1 and 0 are undefined. table 2 gives examples of digital output data and the corres ponding temperature reading for 12-bit resolution conversions. temperature register format figure 3 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 ls byte 2 3 2 2 2 1 2 0 2 -1 2 -2 2 -3 2 -4 bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8 ms byte s s s s s 2 6 2 5 2 4 temperature/data relationship table 2 temperature digital output (binary) digital output (hex) +85c* 0000 0101 0101 0000 0550h +25.0625c 0000 0001 1001 0001 0191h +10.125c 0000 0000 1010 0010 00a2h +0.5c 0000 0000 0000 1000 0008h 0c 0000 0000 0000 0000 0000h -0.5c 1111 1111 1111 1000 fff8h -10.125c 1111 1111 0101 1110 ff5eh -25.0625c 1111 1110 0110 1111 fe6fh -55c 1111 1100 1001 0000 fc90h *the power-on reset value of the temperature register is +85c operation ? alarm signaling after the ds18b20-par performs a temperature convers ion, the temperature value is compared to the user-defined two?s complement alarm trigger values stored in the 1-byte t h and t l registers (see figure 4). the sign bit (s) indicates if the value is positive or ne gative: for positive numbers s = 0 and for negative numbers s = 1. the t h and t l registers are nonvolat ile (eeprom) so they will retain data when the device is powered down. t h and t l can be accessed through bytes 2 and 3 of the scratchpad as explained in the memory s ection of this datasheet. t h and t l register format figure 4 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 s 2 6 2 5 2 4 2 3 2 2 2 1 2 0 only bits 11 through 4 of the temperature register are used in the t h and t l comparison since t h and t l are 8-bit registers. if the result of a temper ature measurement is higher than or equal to t h or lower than or equal to t l , an alarm condition exists and an alarm flag is set inside the ds18b20-par. this flag is updated after every temperature measurement; therefore, if the alarm condition goes away, the flag will be turned off after the next temperature conversion.
ds18b20-par 5 of 19 the master device can check the al arm flag status of all ds ds18b 20-pars on the bus by issuing an alarm search [ech] comma nd. any ds18b20-pars with a set alarm flag will respond to the command, so the master can determine exactly which ds18b20-pa rs have experienced an alarm condition. if an alarm condition exists and the t h or t l settings have changed, another temperature conversion should be done to validate the alarm condition. 64-bit lasered rom code each ds18b20-par contains a unique 64?bit code (see figure 5) stored in rom. the least significant 8 bits of the rom code contain the ds18b20-par?s 1?wire family code: 28h. the next 48 bits contain a unique serial number. the most significant 8 bits c ontain a cyclic redundancy check (crc) byte that is calculated from the first 56 bits of the rom code. a detailed explanation of the crc bits is provided in the crc generation section. the 64?bit rom code and associated rom function control logic allow the ds18b20-par to operate as a 1?wire device using the protocol detailed in the 1-wire bus system section of this datasheet. 64-bit lasered rom code figure 5 8-bit crc 48-bit serial numbe r 8-bit family code (28h) memory the ds18b20-par?s memory is organized as shown in figure 6. the memory consists of an sram scratchpad with nonvolatile eeprom storage for the high and low alarm trigger registers (t h and t l ) and configuration register. note that if th e ds18b20-par alarm function is not used, the t h and t l registers can serve as general-purpose memory. all memory commands are described in detail in the ds18b20-par function commands section. byte 0 and byte 1 of the scratchpad contain the lsb and the msb of the temperature register, respectively. these bytes are read-only. bytes 2 and 3 provide access to t h and t l registers. byte 4 contains the configuration regi ster data, which is explained in detail in the configuration register section of this datasheet. bytes 5, 6 a nd 7 are reserved for internal use by the device and cannot be overwritten. byte 8 of the scratchpad is read-only and contains the cyclic redundancy check (crc) code for bytes 0 through 7 of the scratchpad. the ds18b20-par gene rates this crc using the method described in the crc generation section. data is written to bytes 2, 3, and 4 of the scratchpad using the write scratchpad [4eh] command, and the data must be transmitted to the ds18b20-par starting w ith the least significant bit of byte 2. to verify data integrity, the scratchpad can be read (using th e read scratchpad [beh] command) after the data is written. when reading the scratchpad, data is tran sferred over the 1-wire bus starting with the least significant bit of byte 0. to transfer the t h , t l and configuration data from the scratchpad to eeprom, the master must issue the copy scratchpad [48h] command. data in the eeprom registers is retained when th e device is powered down; at power-up the eeprom data is reloaded into the correspond ing scratchpad locations. data ca n also be reloaded from eeprom to the scratchpad at an y time using the recall e 2 [b8h] command. the master can issue ?read time slots? (see the 1-wire bus system se ction) following the recall e 2 command and the ds18b20-par will indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done. msb msb lsb lsb lsb msb
ds18b20-par 6 of 19 ds18b20-par memory map figure 6 scratchpad (power-up state) byte 0 temperature lsb (50h) byte 1 temperature msb (05h) eeprom byte 2 t h register or user byte 1* t h register or user byte 1 byte 3 t l register or user byte 2* t l register or user byte 2 byte 4 configuration register * configuration register byte 5 reserved (ffh) byte 6 reserved byte 7 reserved (10h) byte 8 crc* * power-up state depends on value(s) stored in eeprom configuration register byte 4 of the scratchpad memory cont ains the configuration register, whic h is organized as illustrated in figure 7. the user can set the conversion resolution of the ds18b20-par using the r0 and r1 bits in this register as shown in table 3. the power-up de fault of these bits is r0 = 1 and r1 = 1 (12-bit resolution). note that there is a direct tradeoff betw een resolution and conversion time. bit 7 and bits 0-4 in the configuration register are reserved for in ternal use by the device an d cannot be overwritten. configuration register figure 7 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 0 r1 r0 1 1 1 1 1 thermometer resoluti on configuration table 3 r1 r0 resolution max conversion time 0 0 9-bit 93.75 ms (t conv /8) 0 1 10-bit 187.5 ms (t conv /4) 1 0 11-bit 375 ms (t conv /2) 1 1 12-bit 750 ms (t conv ) crc generation crc bytes are provided as part of the ds18b20-par?s 64-bit rom code and in the 9 th byte of the scratchpad memory. the rom code crc is calculated from the first 56 bits of the rom code and is contained in the most significant byte of the rom. the scratchpad crc is calculated from the data stored in the scratchpad, and ther efore it changes when the data in the scratchpad changes. the crcs provide the bus master with a method of data validation when data is read from the ds18b20-par. to verify that data has been read correctly, the bus ma ster must re-calculate th e crc from the received data (85c)
ds18b20-par 7 of 19 and then compare this value to e ither the rom code crc (for rom read s) or to the scratchpad crc (for scratchpad reads). if the calculated crc matches the read crc, the data ha s been received error free. the comparison of crc values and the decision to conti nue with an operation are determined entirely by the bus master. there is no circuitry inside the ds18b20-par that prevents a command sequence from proceeding if the ds18b20-par c rc (rom or scratchpad) does not match the value generated by the bus master. the equivalent polynomial function of the crc (rom or scratchpad) is: crc = x 8 + x 5 + x 4 + 1 the bus master can re-calculate the crc and compare it to the crc values from the ds18b20-par using the polynomial generator shown in figure 8. this circuit consists of a shif t register and xor gates, and the shift register bits are initialized to 0. starti ng with the least significant bi t of the rom code or the least significant bit of byte 0 in the scratchpad, one bit at a time should shifted into the shift register. after shifting in the 56 th bit from the rom or the most signifi cant bit of byte 7 fro m the scratchpad, the polynomial generator will contain the re-calculated crc. next, the 8-bit rom code or scratchpad crc from the ds18b20-par must be shifted into the circ uit. at this point, if the re-calculated crc was correct, the shift register will c ontain all 0s. additional informati on about the dallas 1-wire cyclic redundancy check is available in application note 27 entitled ?understanding and using cyclic redundancy checks with dallas semiconductor touch memory products.? crc generator figure 8 1-wire bus system the 1-wire bus system uses a single bus master to control one or more slave devices. the ds18b20- par is always a slave. when there is only one slave on the bus, the system is referred to as a ?single- drop? system; the system is ?multi-drop? if there are multiple slaves on the bus. all data and commands are transmitted least significant bit first over the 1-wire bus. the following discussion of the 1-wire bus system is broken down into three topics: hardware configuration, transact ion sequence, and 1-wire signa ling (signal types and timing). hardware configuration the 1-wire bus has by definition only a single data lin e. each device (master or slave) interfaces to the data line via an open drain or 3?state port. this a llows each device to ?release? the data line when the device is not transmitting data so the bus is availabl e for use by another device. the 1-wire port of the ds18b20-par (the dq pin) is open dr ain with an internal circuit equiva lent to that shown in figure 9. the 1-wire bus requires an external pullup resistor of approximately 5 k ; thus, the idle state for the 1- wire bus is high. if for any reason a transaction needs to be suspended, the bus must be left in the idle state if the transaction is to resume. infinite recovery time can occur between bits so long as the 1-wire bus is in the inactive (high) state during the recovery period. if the bus is held low for more than 480 s, all components on the bus will be reset. in add ition, to assure that the ds18b20-par has sufficient supply current during temperature conversions, it is necessary to provide a strong pullup (such as a mosfet) on the 1-wire bus whenever temperature conversions or eeprom writes are taking place (as described in the parasite power section). (msb) (lsb) xor xor xor input
ds18b20-par 8 of 19 hardware configuration figure 9 transaction sequence the transaction sequence for accessing the ds18b20-par is as follows: step 1. initialization step 2. rom command (followed by any required data exchange) step 3. ds18b20-par function command (followed by any required data exchange) it is very important to follow this sequence ev ery time the ds18b20-par is accessed, as the ds18b20- par will not respond if any st eps in the sequence are missing or out of order. exceptions to this rule are the search rom [f0h] and alarm search [ech] commands. after issuing either of these rom commands, the master must return to step 1 in the sequence. initialization all transactions on the 1-wire bus begin with an initialization sequence. the initialization sequence consists of a reset pulse transmitted by the bus ma ster followed by presence pulse(s) transmitted by the slave(s). the presence pulse lets the bus master know that slave devices (such as the ds18b20-par) are on the bus and are ready to operate. timing for the reset and presence pulses is detailed in the 1-wire signaling section. rom commands after the bus master has detect ed a presence pulse, it can issu e a rom command. these commands operate on the unique 64?bit rom codes of each sl ave device and allow the master to single out a specific device if many are present on the 1-wire bus. these commands also allow the master to determine how many and what types of devices are presen t on the bus or if any de vice has experienced an alarm condition. there are five rom commands, and each command is 8 bits long. the master device must issue an appropriate rom command before issuing a ds18b20-pa r function command. a flowchart for operation of the rom commands is shown in figure 10. search rom [f0h] when a system is initially powered up, the master must identify the ro m codes of all slave devices on the bus, which allows the master to determine the number of slaves and their device types. the master learns the rom codes through a process of elimination that requires the master to perform a search rom v pu 4.7k 5 a typ. r x t x ds18b20-par 1-wire port 100 m os fet t x r x r x = receive t x = transmit 1-wire bus dq pin v pu micro- processor strong pullup
ds18b20-par 9 of 19 cycle (i.e., search rom command followed by data exch ange) as many times as necessary to identify all of the slave devices. if there is only one slave on the bus, the simpler read rom command (see below) can be used in place of the search rom process. for a detailed explan ation of the search rom procedure, refer to the i button ? book of standards at www.ibutton.com/ibuttons/standard.pdf . after every search rom cycle, the bus master must return to step 1 (initialization) in the transaction sequence. read rom [33h] this command can only be used when there is one slave on the bus. it allows the bus master to read the slave?s 64-bit rom code without using the search rom procedure. if this command is used when there is more than one slave present on the bus, a data collision will occur when all the slaves attempt to respond at the same time. match rom [55h] the match rom command followed by a 64?bit rom code sequence allows the bus master to address a specific slave device on a multi-drop or single-drop bus. only the slave that exactly matches the 64?bit rom code sequence will respond to the function command issued by the master; all other slaves on the bus will wait for a reset pulse. skip rom [cch] the master can use this command to address all devi ces on the bus simultaneou sly without sending out any rom code information. for example, the mast er can make all ds18b20- pars on the bus perform simultaneous temperature conversio ns by issuing a skip rom command followed by a convert t [44h] command. note, however, that the skip rom comma nd can only be followed by the read scratchpad [beh] command when there is one sl ave on the bus. this sequence save s time by allowing the master to read from the device without sending its 64?bit rom c ode. this sequence will cause a data collision on the bus if there is more than one slave since multipl e devices will attempt to transmit data simultaneously. alarm search [ech] the operation of this command is identical to the operation of the search rom command except that only slaves with a set alarm flag will respond. this command allows the master device to determine if any ds18b20-pars experienced an alarm condition during the most recent temperature conversion. after every alarm search cycle (i.e., alarm search command followed by data exchange), the bus master must return to step 1 (initiali zation) in the transac tion sequence. refer to the operation ? alarm signaling section for an explan ation of alarm flag operation. ds18b20-par function commands after the bus master has used a rom command to address the ds18b20-par with which it wishes to communicate, the master can issue one of the ds18b20-par function comman ds. these commands allow the master to write to and read from the ds18b20-par?s scratchpad memo ry, initiate temperature conversions and determine the power supply mode. the ds18b20-par functi on commands, which are described below, are summarized in table 4 and illustrated by the flowchart in figure 11. convert t [44h] this command initiates a single te mperature conversion. following th e conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratchpad memory and the ds18b20-par returns to its low-power idle state. within 10 s (max) after this command is i ssued the master must enable a strong pullup on the 1-wire bus for the duration of th e conversion (t conv ) as described in the parasite power section. write scratchpad [4eh] this command allows the master to write 3 bytes of data to the ds18b20-par?s scratchpad. the first data byte is written into the t h register (byte 2 of the scratchpad), the second byte is written into the t l register (byte 3), and the third byte is written into th e configuration register (byte 4). data must be i button is a registered trademark of dallas semiconductor.
ds18b20-par 10 of 19 transmitted least significant bit first. all three bytes must be written befo re the master issues a reset, or the data may be corrupted. read scratchpad [beh] this command allows the master to read the contents of the scratchpad. the data transfer starts with the least significant bit of byte 0 and con tinues through the scratchpad until the 9 th byte (byte 8 ? crc) is read. if only part of the scratchpa d contents is required, the master ma y issue a reset to terminate reading at any time. copy scratchpad [48h] this command copies the contents of the scratchpad t h , t l and configuration registers (bytes 2, 3 and 4) to eeprom. within 10 s (max) after this command is issued the master must enable a strong pullup on the 1-wire bus for at least 10 ms as described in the parasite power section. recall e 2 [b8h] this command recalls the alarm trigger values (t h and t l ) and configuration da ta from eeprom and places the data in bytes 2, 3, and 4, respectively, in the scratchpad memory. the master device can issue ?read time slots? (see the 1-wire bus system section) following the recall e 2 command and the ds18b20-par will indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done. the recall operation happe ns automatically at power-up, so valid data is available in the scratchpad as soon as power is applied to the device. ds18b20-par function command set table 4 command description protocol 1-wire bus activity after command is issued notes temperature conversion commands convert t initiates temperature conversion. 44h none 1 memory commands read scratchpad reads the entire scratchpad including the crc byte. beh ds18b20-par transmits up to 9 data bytes to master. 2 write scratchpad writes data into scratchpad bytes 2, 3, and 4 (t h , t l , and configuration registers). 4eh master transmits 3 data bytes to ds18b20-par. 3 copy scratchpad copies t h , t l , and configuration register data from the scratchpad to eeprom. 48h none 1 recall e 2 recalls t h , t l , and configuration register data from eeprom to the scratchpad. b8h ds18b20-par transmits recall status to master. notes: 1. the master must enable a strong pullup on the 1-wi re bus during temperature conversions and copies from the scratchpad to eeprom. no other bus activity may take place during this time. 2. the master can interrupt the transmission of data at any time by issuing a reset. 3. all three bytes must be written before a reset is issued.
ds18b20-par 11 of 19 rom commands flow chart figure 10 cch skip rom command master t x reset pulse ds18b20-par t x presence pulse master t x rom command 33h read rom command 55h match rom command f0h search rom command ech alarm search command master t x bit 0 bit 0 mat c h? master t x bit 1 bit 1 match? bit 63 match? master t x bit 63 n y y y y y n n n n n n n y y y bit 0 match? bit 1 match? bit 63 match? n n n y y y ds18b20-par t x family code 1 byte ds18b20-par t x serial number 6 bytes ds18b20-par t x crc byte ds18b20-par t x bit 0 ds18b20-par t x bit 0 master t x bit 0 n y device(s) with alarm flag set? initialization sequence master t x function command (figure 11) ds18b20-par t x bit 0 ds18b20-par t x bit 0 master t x bit 0 ds18b20-par t x bit 1 ds18b20-par t x bit 1 master t x bit 1 ds18b20-par t x bit 63 ds18b20-par t x bit 63 master t x bit 63
ds18b20-par 12 of 19 ds18b20-par function co mmands flow chart figure 11 master t x function command y n 44h convert temperature ? master enables strong pullup on dq ds18b20-par converts temperature master disables strong pullup y n 48h copy scratchpad ? master enables strong pull-up on dq data copied from scratchpad to eeprom master disables strong pullup return to initialization sequence (figure 10) for next transaction y n y beh read scratchpad ? have 8 bytes been read ? n master t x reset ? master r x data byte from scratchpad n y master r x scratchpad crc byte master r x ?1s? y n b8h recall e 2 ? master begins data recall from e 2 prom device busy recalling data ? n y master r x ?0s? master t x t h byte to scratchpad y n 4eh write scratchpad ? master t x t l byte to scratchpad master t x config. byte to scratchpad
ds18b20-par 13 of 19 1-wire signaling the ds18b20-par uses a strict 1-wi re communication protocol to insu re data integrity. several signal types are defined by this protocol: re set pulse, presence pulse, write 0, write 1, read 0, and read 1. all of these signals, with the exception of the pres ence pulse, are initiated by the bus master. initialization procedure: reset and presence pulses all communication with the ds18b20-pa r begins with an initi alization sequence that consists of a reset pulse from the master followed by a presence pulse from the ds18b20-par. this is illustrated in figure 12. when the ds18b20-par sends the presence pulse in response to the reset, it is indicating to the master that it is on the bus and ready to operate. during the initialization sequenc e the bus master transmits (t x ) the reset pulse by pulling the 1-wire bus low for a minimum of 480 s. the bus master then releases th e bus and goes into receive mode (r x ). when the bus is released, the 5k pullup resistor pulls the 1-wire bus high. when the ds18b20-par detects this rising edge, it waits 15?60 s and then transmits a presence pulse by pulling the 1-wire bus low for 60?240 s. initialization timing figure 12 read/write time slots the bus master writes data to the ds18b20-par during write time slots and reads data from the ds18b20-par during read time slots. one bit of data is transmitted over the 1-wire bus per time slot. write time slots there are two types of write time slots: ?write 1? tim e slots and ?write 0? time slots. the bus master uses a write 1 time slot to write a logic 1 to the ds18b20-par and a write 0 time slot to write a logic 0 to the ds18b20-par. all write tim e slots must be a minimum of 60 s in duration with a minimum of a 1 s recovery time between individual write slots. both types of write time slots are initiated by the master pulling the 1-wire bus low (see figure 13). to generate a write 1 time slot, afte r pulling the 1-wire bus low, the bus master must release the 1-wire bus within 15 s. when the bus is released, the 5k pullup resistor will pull the bus high. to generate a write 0 time slot, after pulling the 1-wire bus low, the bus master must continue to hold the bus low for the duration of the tim e slot (at least 60 s). line type legend bus master pulling low ds18b20-par pulling low resistor p ullu p v pu gnd 1-wire bus 480 s minimum 480 s master t x reset pulse master r x ds18b20-par waits 15-60 s
ds18b20-par 14 of 19 the ds18b20-par samples the 1-wire bus during a window that lasts from 15 s to 60 s after the master initiates the write time slot. if the bus is high during the sampling window , a 1 is written to the ds18b20-par. if the line is low, a 0 is written to the ds18b20-par. read/write time slot timing diagram figure 13 read time slots the ds18b20-par can only transmit data to the master when the master issues read time slots. therefore, the master must generate read time slot s immediately after issui ng a read scratchpad [beh] command, so that the ds18b20-par can provide the request ed data. in addition, the master can generate read time slots after issuing a recall e 2 [b8h] command to find out the reca ll status as explained in the ds18b20-par function command section. all read time slots must be a minimum of 60 s in duration with a minimum of a 1 s recovery time between slots. a read time slot is initiated by the master device pulling the 1-wire bus low for a minimum of 1 s and then releasing the bus (see figure 13). after the master initiates the read time slot, the ds18b20-par will begin transmitting a 1 or 0 on bus. the ds18b20-par transmits a 1 by leaving the bus high and transmits a 0 by pulling the bus low. when transmitting a 0, the ds18b20-par will release the bus by the end of the time slot, and the bus will be pul led back to its high idle state by the pullup resister. output data fr om the ds18b20-par is valid for 15 s after the falling edge that initiated 45 s 15 s v pu gnd 1-wire bus 60 s < t x ?0? < 120 1 s < t rec < ds18b20-par samples min typ max 15 s 30 min typ max v pu gnd 1-wire bus 15 start of slot > 1 s < t rec < 15 s 15 s 15 line type legend bus master pulling low ds18b20-par pulling low resistor pullup > 1 s
ds18b20-par 15 of 19 the read time slot. therefore, the master must rel ease the bus and then sample the bus state within 15 s from the start of the slot. figure 14 illustrates that the sum of t init , t rc , and t sample must be less than 15 s for a read time slot. figure 15 shows that system timing margin is maximized by keeping t init and t rc as short as possible and by locating the master sample time during read time slots towards the end of the 15 s period. detailed master read 1 timing figure 14 recommended master read 1 timing figure 15 ds18b20-par operation example 1 in this example there are multiple ds18b20-pars on the bus. the bus master initiates a temperature conversion in a specific ds18b20-par and then reads its scratchpad and recalcul ates the crc to verify the data. master mode data (lsb first) comments tx reset master issues reset pulse. rx presence ds18b20-pars respond with presence pulse. tx 55h master issues match rom command. tx 64-bit rom code master sends ds18b20-par rom code. tx 44h master issues convert t command. tx dq line held high by strong pullup master applies strong pullup to dq for the duration of the conversion (t conv ). tx reset master issues reset pulse. rx presence ds18b20-pars respond with presence pulse. tx 55h master issues match rom command. tx 64-bit rom code master sends ds18b20-par rom code. tx beh master issues read scratchpad command. v pu gnd 1-wire bus 15 s master samples line type legend bus master pulling low resistor pullup v pu gnd 1-wire bus 15 master samples
ds18b20-par 16 of 19 master mode data (lsb first) comments rx 9 data bytes master reads entire scratchpad including crc. the master then recalculates the crc of the first eight data bytes from the scratchpad and compares the calculated crc with the read crc (byte 9). if they match, the master continues; if not, the read operation is repeated. ds18b20-par operation example 2 in this example there is only one ds18b20-pa r on the bus. the master writes to the t h , t l , and configuration registers in the ds18b 20-par scratchpad and then reads the scratchpad and recalculates the crc to verify the data. the master then copies the scratchpad c ontents to eeprom. master mode data (lsb first) comments tx reset master issues reset pulse. rx presence ds18b20-par responds with presence pulse. tx cch master issues skip rom command. tx 4eh master issues write scratchpad command. tx 3 data bytes master sends three data bytes to scratchpad (t h , t l , and config). tx reset master issues reset pulse. rx presence ds18b20-par responds with presence pulse. tx cch master issues skip rom command. tx beh master issues read scratchpad command. rx 9 data bytes master reads entire scrat chpad including crc. the master then recalculates the crc of the first eight data bytes from the scratchpad and compares the calculated crc with the read crc (byte 9). if they match, the master continues; if not, the read operation is repeated. tx reset master issues reset pulse. rx presence ds18b20-par responds with presence pulse. tx cch master issues skip rom command. tx 48h master issues copy scratchpad command. tx dq line held high by strong pullup master applies strong pullup to dq for at least 10 ms while copy operation is in progress.
ds18b20-par 17 of 19 absolute maxi mum ratings* voltage on any pin relative to ground ?0.5v to +6.0v operating temperature ?55 c to +100 c storage temperature ?55 c to +125 c soldering temperature s ee j-std-020a specification *these are stress ratings only and functional operati on of the device at these or any other conditions above those indicated in the operatio n sections of this specification is not implied. exposure to absolute maximum rating conditions for extended pe riods of time may affect reliability. dc electrical characteristics (-55c to +100c; v pu =3.0v to 5.5v) parameter symbol condition min typ max units notes pullup supply voltage v pu 3.0 5.5 v 1,2 thermometer error t err -10c to +85c ? -55c to +100c 2 c 3 input logic low v il -0.3 +0.8 v 1,4,5 input logic high v ih 3.0 5.5 v 1,6 sink current i l v i/o =0.4v 4.0 ma 1 active current i dqa 1 1.5 ma 7 dq input current i dq 5 a 8 drift 0.2 c 9 notes: 1. all voltages are referenced to ground. 2. the pullup supply voltage specification assumes that the pullup device (resist or or transistor) is ideal, and therefore the high leve l of the pullup is equal to v pu . in order to meet the v ih spec of the ds18b20-par, the actual supply rail for the strong pu llup transistor must in clude margin for the voltage drop across the transistor when it is turned on; thus: v pu_actual = v pu_ideal + v transistor . 3. see typical performance curve in figure 16. 4. logic low voltages are specified at a sink current of 4 ma. 5. to always guarantee a presence pulse under low voltage parasite power conditions, v ilmax may have to be reduced to as low as 0.5v. 6. logic high voltages are specified at a source current of 1 ma. 7. active current refers to supply current during active temperature conversions or eeprom writes. 8. dq line is high (?hi-z? state). 9. drift data is based on a 1000 hour stress test at 125c. ac electrical characteristics: nv memory (-55c to +100c; v pu =3.0v to 5.5v) parameter symbol condition min typ max units nv write cycle time t wr 2 10 ms eeprom writes n eewr -55c to +55c 50k writes eeprom data retention t eedr -55c to +55c 10 years
ds18b20-par 18 of 19 ac electrical characteristics (-55c to +100c; v pu =3.0v to 5.5v) parameter symbol condition min typ max units notes temperature conversion t conv 9-bit resolution 93.75 ms 1 time 10-bit resolution 187.5 ms 1 11-bit resolution 375 ms 1 12-bit resolution 750 ms 1 time to strong pullup on t spon start convert t or copy scratchpad command issued 10 s time slot t slot 60 120 s 1 recovery time t rec 1 s 1 write 0 low time r low0 60 120 s 1 write 1 low time t low1 1 15 s 1 read data valid t rdv 15 s 1 reset time high t rsth 480 s 1 reset time low t rstl 480 960 s 1,2 presence detect high t pdhigh 15 60 s 1 presence detect low t pdlow 60 240 s 1 capacitance c in/out 25 pf notes: 1. refer to timing diagrams in figure 17. 2. if t rstl > 960 s, a power on reset may occur. typical performance curve figure 16 ds18b20-par typical error curve -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0 10203040506070 reference temp (c) thermometer error (c) mean error +3 error -3 error
ds18b20-par 19 of 19 timing diagrams figure 17

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