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| DS2751 Multichemistry Battery Fuel Gauge www.maxim-ic.com FEATURES Available in Two Configurations - Internal 25mW Sense Resistor - External User-Selectable Sense Resistor Current Measurement - 12-Bit Bidirectional Measurement - Internal Sense Resistor Configuration: 0.625mA LSB and 1.9A Dynamic Range - External Sense Resistor Configuration: 15.625mV LSB and 64mV Dynamic Range Current Accumulation - Internal Sense Resistor: 0.25mAhr LSB - External Sense Resistor: 6.25mVhr LSB Voltage Measurement with 4.88mV Resolution Temperature Measurement Using Integrated Sensor with 0.125C Resolution 32 Bytes of Lockable EEPROM 16 Bytes of General-Purpose SRAM Dallas 1-Wire(R) Interface with Unique 64-Bit Device Address Supports 1-Cell Li+/Polymer or 3-Cell Ni Battery Packs 3mm Dimension of 8-Pin TSSOP Package Allows Mounting on Side of Thin Li+ and Li+/Polymer Cells (Lead Free available) Low Power Consumption: - Active Current: 60mA (typ), 90mA (max) - Sleep Current: 1mA (typ), 2mA (max) PIN CONFIGURATION VIN VSS PIO VDD 1 2 2 3 2 4 8 7 6 5 DQ SNS IS2 IS1 DS2751E 8-Pin TSSOP Package (Lead Free Available) PIN DESCRIPTION VIN VSS PIO VDD IS1 IS2 SNS DQ Voltage-Sense Input Device Ground Programmable I/O Pin Power-Supply Input (2.5V to 5.5V) Current-Sense Input Current-Sense Input Sense Resistor Connection Data Input/Output 1-Wire is a registered trademark of Dallas Semiconductor. 1 of 19 020105 DS2751 ORDERING INFORMATION MARKING TEMP RANGE DESCRIPTION 8-Pin TSSOP, External Sense Resistor 2751E -20C to +70C 2751E 8-Pin Lead Free TSSOP, External Sense DS2751E+ -20C to +70C (Note 1) Resistor DS2751E-025 2751R -20C to +70C 8-Pin TSSOP, 25mW Sense Resistor 2751R 8-Pin Lead Free TSSOP, 25mW Sense DS2751E+025 -20C to +70C (Note 1) Resistor DS2751E on Tape-and-Reel DS2751E/T&R 2751E -20C to +70C 2751E DS2751E+ on Tape-and-Reel (Lead Free) DS2751E+T&R -20C to +70C (Note 1) DS2751E-025 on Tape-and-Reel DS2751E-025/T&R 2751R -20C to +70C 2751R DS2751E+025 on Tape-and-Reel (Lead DS2751E+025/T&R -20C to +70C (Note 1) Free) Note 1: A "+" will be marked on the package near the Pin 1 indicator. PART DS2751E DESCRIPTION The DS2751 multichemistry battery fuel gauge is a data-acquisition and information-storage device tailored for cost-sensitive and space-constrained 1-cell Li+/polymer or 3-cell Ni battery-pack applications. The DS2751 provides the key hardware components required to accurately estimate remaining capacity by integrating low-power, precision measurements of temperature, voltage, current, and current accumulation, as well as nonvolatile (NV) data storage, into the small footprint of a 3.0mm x 4.4mm 8-pin TSSOP package. Through its 1-Wire interface, the DS2751 gives the host system read/write access to status and control registers, instrumentation registers, and general-purpose data storage. Each device has a unique factoryprogrammed 64-bit net address that allows it to be individually addressed by the host system, supporting multibattery operation. The DS2751 performs temperature, voltage, and current measurement to a resolution sufficient to support process-monitoring applications such as battery charge control and remaining capacity estimation. Temperature is measured using an on-chip sensor, eliminating the need for a separate thermistor. Bidirectional current measurement and accumulation are accomplished using either an internal 25mW sense resistor or an external device. The DS2751 also features a programmable I/O pin that allows the host system to sense and control other electronics in the pack, including switches, vibration motors, speakers, and LEDs. Three types of memory are provided on the DS2751 for battery information storage: EEPROM, lockable EEPROM, and SRAM. EEPROM memory saves important battery data in true NV memory that is unaffected by severe battery depletion, accidental shorts, or ESD events. Lockable EEPROM becomes ROM when locked to provide additional security for unchanging battery data. SRAM provides inexpensive storage for temporary data. 2 of 19 DS2751 ABSOLUTE MAXIMUM RATINGS* Voltage on PIO Pin, Relative to VSS Voltage on All Other Pins, Relative to VSS Continuous Internal Sense Resistor Current Pulsed Internal Sense Resistor Current Operating Temperature Range Storage Temperature Range Soldering Temperature -0.3V to +12V -0.3V to +6V 2.5A 50A for <100s/s, <1000 Pulses -40C to +85C -55C to +125C See J-STD-020A Specification * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. RECOMMENDED DC OPERATING CONDITIONS (TA = 2.5V VDD 5.5V, -20C to +70C.) PARAMETER SYMBOL CONDITIONS Supply Voltage VDD (Note 1) Data Pin DQ (Note 1) VDD 4.2V (Notes 1, 2) VIN Pin VIN 2.5V < VDD < 4.2V (Notes 1, 2) MIN 2.5 -0.3 -0.3 TYP MAX 5.5 +5.5 +4.5 VDD + 0.3 UNITS V V V V DC ELECTRICAL CHARACTERISTICS (TA = 2.5V VDD 5.5V, -20C to +70C.) PARAMETER SYMBOL CONDITIONS DQ = VDD, Active Current IACTIVE normal operation DQ = 0V, Sleep-Mode Current ISLEEP no activity Input Logic High: VIH (Note 1) DQ, PIO Input Logic Low: VIL (Note 1) DQ, PIO Output Logic Low: IOL = 4mA (Note 1) VOL DQ, PIO DQ Pulldown Current IPD Input Resistance: VIN RIN Internal Current-Sense RSNS +25C Resistor DQ Low-to-Sleep tSLEEP Time Undervoltage Detect VUV (Note 1) Undervoltage Delay TUVD MIN TYP 60 1 1.5 0.4 0.4 1 5 20 2.2 2.5 90 2.6 100 2.7 110 25 30 MAX 90 2 UNITS mA mA V V V mA MW mW s V ms 3 of 19 DS2751 ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT (TA = 2.5V VDD 5.5V, -20C to +70C.) PARAMETER SYMBOL CONDITIONS Temperature Resolution TLSB Temperature Full-Scale TFS Magnitude Temperature Error TERR (Note 3) Voltage Resolution VLSB Voltage Full-Scale (Note 4) VFS Magnitude Voltage Offset Error VOERR (Note 5) Voltage Gain Error Current Resolution Current Full-Scale Magnitude Current Offset Error Current Gain Error Accumulated Current Resolution Current Sampling Frequency Internal Timebase Accuracy VGERR ILSB IFS IOERR IGERR qCA fSAMP tERR 0C to +50C (Note 11) -20C to +70C (Note 6) (Note 7) (Notes 6, 7) (Note 8) (Note 9) (Notes 6, 10) (Note 7) (Note 6) (Note 7) 0.625 15.625 2.56 64 1 3 1 0.25 6.25 1456 1 3 5 MIN 127 4.88 4.5 1 3 3 TYP 0.125 MAX UNITS C C C mV V LSB %V reading mA mV 1.9 A mV LSB %I reading mAhr Vhr Hz % ELECTRICAL CHARACTERISTICS--1-WIRE INTERFACE (TA = 2.5V VDD 5.5V, -20C to +70C.) PARAMETER SYMBOL CONDITIONS Time Slot tSLOT Recovery Time tREC Write 0 Low Time tLOW0 Write 1 Low Time tLOW1 Read Data Valid tRDV Reset Time High tRSTH Reset Time Low tRSTL Presence-Detect High tPDH Presence-Detect Low tPDL DQ Capacitance CDQ MIN 60 1 60 1 480 480 15 60 TYP MAX 120 119 15 15 960 60 240 60 UNITS ms ms ms ms ms ms ms ms ms pF 4 of 19 DS2751 EEPROM RELIABILITY SPECIFICATION (TA = 2.5V VDD 5.5V, -20C to +70C.) PARAMETER SYMBOL CONDITIONS Copy to EEPROM Time tEEC EEPROM Copy (Note 12) NEEC Endurance MIN 25,000 TYP 2 MAX 10 UNITS ms cycles Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: All voltages are referenced to VSS. Operating VIN > 4.5V relative to VSS, or VIN > VDD + 0.3V can induce errors in voltage, temperature, or current measurements. Self heating due to output pin loading and sense resistor power dissipation can alter the reading from ambient conditions. Although the Voltage Register is large enough to report values larger than 4.75V, the internal compensation for circuit variations can reduce the maximum reportable voltage to as low as 4.75V. Voltage offset measurement is with respect to 4.35V at +25C. Internal current-sense resistor configuration. External current-sense resistor configuration. The Current Register supports measurement magnitudes up to 2.56A using the internal senseresistor option and 64mV with the external resistor option. Compensation of the internal sense-resistor value for process and temperature variation may reduce the maximum reportable magnitude to 1.9A. Current offset error null to 1 LSb typically requires a one time 3.5s in-system calibration by user. Current gain-error specification applies to gain error in converting the voltage difference at IS1 and IS2, and excludes any error remaining after the DS2751 compensates for the internal sense-resistor's temperature coefficient of 3700ppm/C to an accuracy of 500ppm/C. The DS2751 does not compensate for external sense resistor characteristics, and any error terms arising from the use of an external sense resistor should be taken into account when calculating total current measurement error. Typical value for tERR valid at 3.6V and +25C. Four year data retention at +70C. 5 of 19 DS2751 Figure 1. FUNCTIONAL DIAGRAM DQ 1-WIRE INTERFACE AND ADDRESS THERMAL SENSE VIN IS1 IS2 MUX VOLTAGE REFERENCE ADC REGISTERS AND USER MEMORY LOCKABLE EEPROM SRAM TEMPERATURE VOLTAGE CURRENT ACCUM. CURRENT STATUS/CONTROL TIMEBASE PIO + - INTERNAL SENSE RESISTOR CONFIGURATION ONLY 25mW SNS CHIP GROUND VSS IS2 IS1 6 of 19 DS2751 Figure 2. APPLICATION EXAMPLE PACK+ 1kW DS2751 150W DATA 5.6V 102 PACKRSNS (1) 150W VIN SNS DQ IS2 VDD PIO VSS IS1 1-CELL Li+ OR 3-CELL Ni 104 5.6V PROTECTOR IC 104 (Li+/POLYMER ONLY) 2.5V RSENSINT SNS 4.7kW (2) VSS 4.7kW RKS IS2 RKS IS1 VOLTAGE SENSE DS2751 1) RSENS is present for external sense resistor configurations only. 2) RSENSINT is present for internal sense resistor configurations only. POWER MODES The DS2751 has two power modes: active and sleep. While in active mode, the DS2751 continuously measures current, voltage, and temperature to provide data to the host system to support current accumulation. In sleep mode, the DS2751 ceases these activities. The DS2751 enters sleep mode when PMOD = 1 and either of the following occur: the DQ line is low for longer than tSLEEP (2.2s) (pack disconnection). the UVEN bit in the Status Register is set to 1 and the voltage on VIN drops below undervoltage threshold VUV for tUVD (cell depletion) The DS2751 returns to active mode when the DQ line is pulled from a low-to-high state and the voltage on VIN is above VUV. The factory default for the DS2751 is UVEN = PMOD = 0. The DS2751 defaults to active mode when power is first applied. 7 of 19 DS2751 CURRENT MEASUREMENT In the active mode of operation, the DS2751 continually measures the current flow into and out of the battery by measuring the voltage drop across a current-sense resistor. The DS2751 is available in two configurations: 1) internal 25mW current-sense resistor, and 2) external user-selectable sense resistor. In either configuration, the DS2751 considers the voltage difference between pins IS1 and IS2 (VIS = VIS1 VIS2) to be the filtered voltage drop across the sense resistor. A positive VIS value indicates current is flowing into the battery (charging), while a negative VIS value indicates current is flowing out of the battery (discharging). VIS is measured with a signed resolution of 12 bits. The Current Register is updated in two's-complement format every 88ms with an average of 128 measurements. Currents outside the range of the register are reported at the limit of the range. The format of the Current Register is shown in Figure 3. For the internal sense resistor configuration, the DS2751 maintains the Current Register in units of amps, with a resolution of 0.625mA and full-scale range of no less than 1.9A (see Note 7 on IFS spec for more details). The DS2751 automatically compensates for internal sense-resistor process variations and temperature effects when reporting current. For the external sense resistor configuration, the DS2751 updates the measured VIS voltage to the Current Register in units of volts, with a resolution of 15.625mV and a 64mV full-scale range. Figure 3. CURRENT REGISTER FORMAT MSB--Address 0E S MSb 211 210 29 28 27 26 25 LSb 24 MSb 23 LSB--Address 0F 22 21 20 X X X LSb Units: 0.625mA for internal sense resistor 15.625mV for external sense resistor CURRENT ACCUMULATOR The Current Accumulator facilitates remaining capacity estimation by tracking the net current flow into and out of the battery. Current flow into the battery increments the Current Accumulator, while current flow out of the battery decrements it. Data is maintained in the Current Accumulator in two'scomplement format. The format of the Current Accumulator is shown in Figure 4. When the internal sense resistor is used, the DS2751 maintains the Current Accumulator in units of amphours, with a resolution of 0.25mAhrs and a 8.2Ahrs full-scale range. When using an external sense resistor, the DS2751 maintains the Current Accumulator in units of volt-hours, with a resolution of 6.25mVhrs and a 205mVhrs full-scale range. The Current Accumulator is a read/write register that can be altered by the host system as needed. 8 of 19 DS2751 Figure 4. CURRENT ACCUMULATOR FORMAT MSB--Address 10 S MSb 214 213 212 211 210 29 28 LSb 27 MSb 26 LSB--Address 11 25 24 23 22 21 20 LSb Units: 0.25mAhrs for internal sense resistor 6.25mVhrs for external sense resistor CURRENT OFFSET COMPENSATION Current measurement and the current accumulation are both internally compensated for offset on a continual basis minimizing error resulting from variations in device temperature and voltage. Additionally, a constant bias can be utilized to alter any other sources of offset. This bias resides in EEPROM address 33h in two's-complement format and is subtracted from each current measurement. The current offset bias is applied to both the internal and external sense resistor configurations. The factory default for the current offset bias is a value of 0. Figure 5. CURRENT OFFSET BIAS Address 33 S MSb 26 25 24 23 22 21 20 LSb Units: 0.625mA for internal sense resistor 15.625mV for external sense resistor VOLTAGE MEASUREMENT The DS2751 continually measures the voltage between pins VIN and VSS over a 0 to 4.5V range. The Voltage Register is updated in two's-complement format every 3.4ms with a resolution of 4.88mV. Voltages above the maximum register value are reported as the maximum value. The Voltage Register format is shown in Figure 6. Figure 6. VOLTAGE REGISTER FORMAT MSB--Address 0C S MSb 29 28 27 26 25 24 23 LSb 22 MSb 21 LSB--Address 0D 20 X X X X X LSb Units: 4.88 mV 9 of 19 DS2751 TEMPERATURE MEASUREMENT The DS2751 uses an integrated temperature sensor to continually measure battery temperature. Temperature measurements are updated in the Temperature Register every 220ms in two's-complement format with a resolution of 0.125C over a 127C range. The Temperature Register format is shown in Figure 7. Figure 7. TEMPERATURE REGISTER FORMAT MSB--Address 18 S MSb 29 28 27 26 25 24 23 LSb 22 MSb 21 LSB--Address 19 20 X X X X X LSb Units: 0.125C PROGRAMMABLE I/O To use the PIO pin as an output, write the desired output value to the PIO bit in the Special Feature Register. Writing a 0 to the PIO bit enables the PIO output driver, pulling the PIO pin to VSS. Writing a 1 to the PIO bit disables the output driver, allowing the PIO pin to be pulled high or used as an input. To sense the value on the PIO pin, read the PIO bit. The DS2751 turns off the PIO output driver and sets the PIO bit high when in sleep mode or when DQ is low for more than tSLEEP (2.2s), regardless of the state of the PMOD bit. MEMORY The DS2751 has a 256-byte linear address space with registers for instrumentation, status, and control in the lower 32 bytes, with lockable EEPROM and SRAM memory occupying portions of the remaining address space. All EEPROM and SRAM memory is general-purpose except addresses 31h and 33h, which should be written with the default values for the Status Register and Current Offset Register, respectively. When the MSB of any two-byte register is read, both the MSB and LSB are latched and held for the duration of the Read Data command to prevent updates during the read and to ensure synchronization between the two register bytes. For consistent results, always read the MSB and the LSB of a two-byte register during the same Read Data command sequence. EEPROM memory is shadowed by RAM to eliminate programming delays between writes and to allow the data to be verified by the host system before being copied to EEPROM. All reads and writes to/from EEPROM memory actually access the shadow RAM. In unlocked EEPROM blocks, the Write Data command updates shadow RAM. In locked EEPROM blocks, the Write Data command is ignored. The Copy Data command copies the contents of shadow RAM to EEPROM in an unlocked block of EEPROM but has no effect on locked blocks. The Recall Data command copies the contents of a block of EEPROM to shadow RAM regardless of whether the block is locked or not. 10 of 19 DS2751 Table 3. MEMORY MAP ADDRESS (HEX) 00 01 02 to 06 07 08 09 to 0B 0C 0D 0E 0F 10 11 12 to 17 18 19 1A to 1F 20 to 2F 30 to 3F 40 to 7F 80 to 8F 90 to FF DESCRIPTION Reserved Status Register Reserved EEPROM Register Special Feature Register Reserved Voltage Register MSB Voltage Register LSB Current Register MSB Current Register LSB Accumulated Current Register MSB Accumulated Current Register LSB Reserved Temperature Register MSB Temperature Register LSB Reserved EEPROM, block 0 EEPROM, block 1 Reserved SRAM Reserved READ/WRITE R R/W R/W R R R R R/W R/W R R R/W* R/W* R/W *Each EEPROM block is read/write until locked by the LOCK command, after which it is read-only. STATUS REGISTER The default values for the Status Register bits are stored in lockable EEPROM in the corresponding bits of address 31h. A Recall Data command for EEPROM block 1 recalls the default values into the Status Register bits. The format of the Status Register is shown in Figure 8. The function of each bit is described in detail in the following paragraphs. Figure 8. STATUS REGISTER FORMAT Address 01 bit 7 X bit 6 X bit 5 bit 4 bit 3 bit 2 X bit 1 X bit 0 X PMOD RNAOP UVEN PMOD--Sleep Mode Enable. A value of 1 in this bit enables the DS2751 to enter sleep mode when the DQ line goes low for greater than tSLEEP. A value of 0 disables the DS2751 from entering the sleep mode. This bit is read-only. The desired default value should be set in bit 5 of address 31h. The factory default is 0. RNAOP--Read Net Address Opcode. A value of 0 in this bit sets the opcode for the Read Net Address command to 33h, while a 1 sets the opcode to 39h. This bit is read-only. The desired default value should be set in bit 4 of address 31h. The factory default is 0. 11 of 19 DS2751 UVEN--Undervoltage Sleep Enable. A value of 1 in UVEN along with a value of 1 in PMOD enables the DS2751 to enter sleep mode when the voltage on VIN drops below undervoltage threshold VUV for tUVD (cell depletion). A value of 0 disables the DS2751 from entering the sleep mode due to undervoltage events. This bit is read-only. The desired default value should be set in bit 3 of address 31h. The factory default is 0. X--Reserved Bits. EEPROM REGISTER The format of the EEPROM Register is shown in Figure 9. The function of each bit is described in detail in the following paragraphs. Figure 9. EEPROM REGISTER FORMAT Address 07 bit 7 EEC bit 6 LOCK bit 5 X bit 4 X bit 3 X bit 2 X bit 1 BL1 bit 0 BL0 EEC--EEPROM Copy Flag. A 1 in this read-only bit indicates that a Copy Data command is in progress. While this bit is high, writes to EEPROM addresses are ignored. A 0 in this bit indicates that data can be written to unlocked EEPROM blocks. LOCK--EEPROM Lock Enable. When this bit is 0, the Lock command is ignored. Writing a 1 to this bit enables the Lock command. After the Lock command is executed, the LOCK bit is reset to 0. The factory default is 0. BL1--EEPROM Block 1 Lock Flag. A 1 in this read-only bit indicates that EEPROM block 1 (addresses 30 to 3F) is locked (read-only), while a 0 indicates block 1 is unlocked (read/write). BL0--EEPROM Block 0 Lock Flag. A 1 in this read-only bit indicates that EEPROM block 0 (addresses 20 to 2F) is locked (read-only), while a 0 indicates block 0 is unlocked (read/write). X--Reserved Bits. SPECIAL FEATURE REGISTER The format of the Special Feature Register is shown in Figure 10. The function of each bit is described in detail in the following paragraphs. Figure 10. SPECIAL FEATURE REGISTER FORMAT Address 08 bit 7 POR bit 6 PIO bit 5 X bit 4 X bit 3 X bit 2 X bit 1 X bit 0 X 12 of 19 DS2751 POR--POR Indicator bit. This bit is set to a 1 when the DS2751 experiences a power-on-reset (POR) event. To use the POR bit to detect a power-on-reset, the POR bit must be set to a 0 by the host system upon power-up and after each subsequent occurrence of a POR. PIO--PIO Pin Sense and Control. See the Programmable I/O section for details on this read/write bit. X--Reserved Bits. 1-WIRE BUS SYSTEM The 1-Wire bus is a system that has a single bus master and one or more slaves. A multidrop bus is a 1Wire bus with multiple slaves. A single-drop bus has only one slave device. In all instances, the DS2751 is a slave device. The bus master is typically a microprocessor in the host system. The discussion of this bus system consists of four topics: 64-Bit Net Address, Hardware Configuration, Transaction Sequence, and 1-Wire Signaling. 64-BIT NET ADDRESS Each DS2751 has a unique, factory-programmed 1-Wire net address that is 64 bits in length. The first 8 bits are the 1-Wire family code (51h for DS2751). The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits (see Figure 11). The 64-bit net address and the 1-Wire I/O circuitry built into the device enable the DS2751 to communicate through the 1-Wire protocol detailed in the 1-Wire Bus System section of this data sheet. Figure 11. 1-WIRE NET ADDRESS FORMAT 8-Bit CRC MSb 48-Bit Serial Number 8-Bit Family Code (51h) LSb CRC GENERATION The DS2751 has an 8-bit CRC stored in the most significant byte of its 1-Wire net address. To ensure error-free transmission of the address, the host system can compute a CRC value from the first 56 bits of the address and compare it to the CRC from the DS2751. The host system is responsible for verifying the CRC value and taking action as a result. The DS2751 does not compare CRC values and does not prevent a command sequence from proceeding as a result of a CRC mismatch. Proper use of the CRC can result in a communication channel with a very high level of integrity. The CRC can be generated by the host using a circuit consisting of a Shift Register and XOR gates as shown in Figure 12, or it can be generated in software. Additional information about the Dallas 1-Wire CRC is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor Touch Memory Products. In the circuit in Figure 12, the shift bits are initialized to 0. Then, starting with the least significant bit of the family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number is entered. After the 48th bit of the serial number has been entered, the Shift Register contains the CRC value. 13 of 19 DS2751 Figure 12. 1-WIRE CRC GENERATION BLOCK DIAGRAM INPUT MSb XOR XOR LSb XOR HARDWARE CONFIGURATION Because the 1-Wire bus has only a single line, it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must connect to the bus with open-drain or tri-state output drivers. The DS2751 uses an open-drain output driver as part of the bidirectional interface circuitry shown in Figure 13. If a bidirectional pin is not available on the bus master, separate output, and input pins can be connected together. The 1-Wire bus must have a pullup resistor at the bus-master end of the bus. For short line lengths, the value of this resistor should be approximately 5kW. The idle state for the 1-Wire bus is high. If, for any reason, a bus transaction must be suspended, the bus must be left in the idle state in order to properly resume the transaction later. If the bus is left low for more than 120ms, slave devices on the bus begin to interpret the low period as a reset pulse, effectively terminating the transaction. Figure 13. 1-WIRE BUS INTERFACE CIRCUITRY BUS MASTER VPULLUP (2.0V to 5.5V) 4.7kW Rx 1mA Typ. Rx = RECEIVE Tx = TRANSMIT 100W MOSFET Rx DS2751 1-WIRE PORT Tx Tx TRANSACTION SEQUENCE The protocol for accessing the DS2751 through the 1-Wire port is as follows: Initialization Net Address Command Function Command Transaction/Data The sections that follow describe each of these steps in detail. 14 of 19 DS2751 All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the bus master followed by a presence pulse simultaneously transmitted by the DS2751 and any other slaves on the bus. The presence pulse tells the bus master that one or more devices are on the bus and ready to operate. For more details, see the I/O Signaling section. NET ADDRESS COMMANDS Once the bus master has detected the presence of one or more slaves, it can issue one of the net address commands described in the following paragraphs. The name of each ROM command is followed by the 8-bit opcode for that command in square brackets. Figure 14 presents a transaction flowchart of the net address commands. Read Net Address [33h or 39h]. This command allows the bus master to read the DS2751's 1-Wire net address. This command can only be used if there is a single slave on the bus. If more than one slave is present, a data collision occurs when all slaves try to transmit at the same time (open drain produces a wired-AND result). The RNAOP bit in the Status Register selects the opcode for this command, with RNAOP = 0 indicating 33h and RNAOP = 1 indicating 39h. Match Net Address [55h]. This command allows the bus master to specifically address one DS2751 on the 1-Wire bus. Only the addressed DS2751 responds to any subsequent function command. All other slave devices ignore the function command and wait for a reset pulse. This command can be used with one or more slave devices on the bus. Skip Net Address [CCh]. This command saves time when there is only one DS2751 on the bus by allowing the bus master to issue a function command without specifying the address of the slave. If more than one slave device is present on the bus, a subsequent function command can cause a data collision when all slaves transmit data at the same time. Search Net Address [F0h]. This command allows the bus master to use a process of elimination to identify the 1-Wire net addresses of all slave devices on the bus. The search process involves the repetition of a simple three-step routine: read a bit, read the complement of the bit, then write the desired value of that bit. The bus master performs this simple three-step routine on each bit location of the net address. After one complete pass through all 64 bits, the bus master knows the address of one device. The remaining devices can then be identified on additional iterations of the process. See Chapter 5 of the Book of DS19xx iButton(R) Standards for a comprehensive discussion of a net address search, including an actual example. This publication can be found on the Maxim/Dallas website at www.maxim-ic.com. FUNCTION COMMANDS After successfully completing one of the net address commands, the bus master can access the features of the DS2751 with any of the function commands described in the following paragraphs. The name of each function is followed by the 8-bit opcode for that command in square brackets. Read Data [69h, XX]. This command reads data from the DS2751 starting at memory address XX. The LSb of the data in address XX is available to be read immediately after the MSb of the address has been entered. Because the address is automatically incremented after the MSb of each byte is received, the LSb of the data at address XX + 1 is available to be read immediately after the MSb of the data at address XX. If the bus master continues to read beyond address FFh, the DS2751 outputs logic 1 until a reset pulse occurs. Addresses labeled "reserved" in the memory map contain undefined data. The Read Data command can be terminated by the bus master with a reset pulse at any bit boundary. iButton is a registered trademark of Dallas Semiconductor. 15 of 19 DS2751 Write Data [6Ch, XX]. This command writes data to the DS2751 starting at memory address XX. The LSb of the data to be stored at address XX can be written immediately after the MSb of the address has been entered. Because the address is automatically incremented after the MSb of each byte is written, the LSb to be stored at address XX + 1 can be written immediately after the MSb to be stored at address XX. If the bus master continues to write beyond address FFh, the DS2751 ignores the data. Writes to readonly addresses, reserved addresses and locked EEPROM blocks are ignored. Incomplete bytes are not written. Writes to unlocked EEPROM blocks are to shadow RAM rather than EEPROM. See the Memory section for more details. Copy Data [48h, XX]. This command copies the contents of shadow RAM to EEPROM for the 16-byte EEPROM block containing address XX. Copy Data commands that address locked blocks are ignored. While the Copy Data command is executing, the EEC bit in the EEPROM Register is set to 1 and writes to EEPROM addresses are ignored. Reads and writes to non-EEPROM addresses can still occur while the copy is in progress. The Copy Data command execution time, tEEC, is 2ms typical and starts after the last address bit is transmitted. Recall Data [B8h, XX]. This command recalls the contents of the 16-byte EEPROM block containing address XX to shadow RAM. Lock [6Ah, XX]. This command locks (write-protects) the 16-byte block of EEPROM memory containing memory address XX. The LOCK bit in the EEPROM Register must be set to l before the Lock command is executed. If the LOCK bit is 0, the Lock command has no effect. The Lock command is permanent; a locked block can never be written again. Table 4. FUNCTION COMMANDS COMMAND Read Data Write Data Copy Data Recall Data Lock DESCRIPTION Reads data from memory starting at address XX Writes data to memory starting at address XX Copies shadow RAM data to EEPROM block containing address XX Recalls EEPROM block containing address XX to shadow RAM Permanently locks the block of EEPROM containing address XX COMMAND PROTOCOL 69h, XX 6Ch, XX 48h, XX B8h, XX 6Ah, XX BUS STATE AFTER COMMAND PROTOCOL Master Rx Master Tx Bus idle Bus idle Bus idle BUS DATA Up to 256 bytes of data Up to 256 bytes of data None None None 16 of 19 DS2751 Figure 14. NET ADDRESS COMMAND FLOW CHART MASTER Tx RESET PULSE DS2751 Tx PRESENCE PULSE MASTER Tx NET ADDRESS COMMAND 33h / 39h READ NO 55h MATCH NO F0h SEARCH NO CCh SKIP NO YES DS2751 Tx FAMILY CODE 1 BYTE YES MASTER Tx BIT 0 YES DS2751 Tx BIT 0 DS2751 Tx BIT 0 MASTER Tx BIT 0 YES MASTER Tx FUNCTION COMMAND DS2751 Tx SERIAL NUMBER 6 BYTES BIT 0 MATCH ? DS2751 Tx CRC 1 BYTE NO NO BIT 0 MATCH ? YES MASTER Tx BIT 1 YES DS2751 Tx BIT 1 DS2751 Tx BIT 1 MASTER Tx BIT 1 BIT 1 MATCH ? NO NO BIT 1 MATCH ? YES YES MASTER Tx BIT 63 DS2751 Tx BIT 63 DS2751 Tx BIT 63 MASTER Tx BIT 63 MASTER Tx FUNCTION COMMAND YES BIT 63 MATCH ? NO 17 of 19 DS2751 I/O SIGNALING The 1-Wire bus requires strict signaling protocols to insure data integrity. The four protocols used by the DS2751 are: the initialization sequence (reset pulse followed by presence pulse), Write 0, Write 1, and Read Data. All of these types of signaling except the presence pulse are initiated by the bus master. The initialization sequence required to begin any communication with the DS2751 is shown in Figure 15. A presence pulse following a reset pulse indicates the DS2751 is ready to accept a net address command. The bus master transmits (Tx) a reset pulse for tRSTL. The bus master then releases the line and goes into receive mode (Rx). The 1-Wire bus line is then pulled high by the pullup resistor. After detecting the rising edge on the DQ pin, the DS2751 waits for tPDH and then transmits the Presence Pulse for tPDL. Figure 15. 1-WIRE INITIALIZATION SEQUENCE tRSTL tPDH DQ PACK- LINE TYPE LEGEND: BUS MASTER ACTIVE LOW BOTH BUS MASTER AND DS2751 ACTIVE LOW DS2751 ACTIVE LOW RESISTOR PULLUP tRSTH tPDL PACK+ WRITE TIME SLOTS A write time slot is initiated when the bus master pulls the 1-Wire bus from a logic high (inactive) level to a logic low level. There are two types of write time slots: Write 1 and Write 0. All write time slots must be tSLOT (60ms to 120ms) in duration with a 1ms minimum recovery time, tREC, between cycles. The DS2751 samples the 1-Wire bus line between 15ms and 60ms after the line falls. If the line is high when sampled, a Write 1 occurs. If the line is low when sampled, a Write 0 occurs (see Figure 16). For the bus master to generate a Write 1 time slot, the bus line must be pulled low and then released, allowing the line to be pulled high within 15ms after the start of the write time slot. For the host to generate a Write 0 time slot, the bus line must be pulled low and held low for the duration of the write time slot. READ TIME SLOTS A read time slot is initiated when the bus master pulls the 1-Wire bus line from a logic high level to a logic low level. The bus master must keep the bus line low for at least 1ms and then release it to allow the DS2751 to present valid data. The bus master can then sample the data tRDV (15ms) from the start of the read time slot. By the end of the read time slot, the DS2751 releases the bus line and allows it to be pulled high by the external pullup resistor. All read time slots must be tSLOT (60ms to 120ms) in duration with a 1ms minimum recovery time, tREC, between cycles. See Figure 16 for more information. 18 of 19 DS2751 Figure 16. 1-WIRE WRITE AND READ TIME SLOTS WRITE 0 SLOT WRITE 1 SLOT tSLOT tLOW0 tREC DQ tLOW1 tSLOT PACK+ PACK- DS2751 SAMPLE WINDOW MIN TYP MAX 15ms 15ms 30ms >1ms 15ms DS2751 SAMPLE WINDOW MIN TYP MAX 15ms 30ms READ 0 SLOT READ 1 SLOT tSLOT tREC tSLOT PACK+ DQ PACK- MASTER SAMPLE WINDOW >1ms MASTER SAMPLE WINDOW tRDV LINE TYPE LEGEND: BUS MASTER ACTIVE LOW BOTH BUS MASTER AND DS2751 ACTIVE LOW tRDV DS2751 ACTIVE LOW RESISTOR PULLUP 19 of 19 |
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