DS75LX Digital Thermometer and Thermostat with Extended Addressing www.maxim-ic.com GENERAL DESCRIPTION FEATURES This low-voltage (1.7V to 3.7V) digital thermometer and thermostat provides 9, 10, 11, or 12-bit digital temperature readings over a -55°C to +125°C range with ±2°C accuracy over a -25°C to +100°C range. At power-up, the DS75LX defaults to 9-bit resolution for software compatibility with the LM75. Communication with the DS75LX is achieved through a simple 2-wire serial interface. Three tri-state address pins allow up to 27 DS75LX devices to operate on the same 2-wire bus, which greatly simplifies distributed temperaturesensing applications. The DS75LX thermostat has a dedicated open-drain output (O.S.) and programmable fault tolerance, which allow the user to define the number of consecutive error conditions that must occur before O.S. is activated. There are two thermostatic operating modes that control thermostat operation based on user-defined trip-points (TOS and THYST). 1.7V to 3.7V Operating Range Tri-State Address Pins Allow Up to 27 Unique Bus Addresses Temperature Measurements Require No External Components Measures Temperatures from -55°C to +125°C (-67°F to +257°F) ±2°C Accuracy from -25°C to +100°C Thermometer Resolution Is UserConfigurable from 9 (Default) to 12 Bits (0.5°C to 0.0625°C Resolution) 9-Bit Conversion Time is 25ms (max) Thermostatic Settings are User-Definable Data is Read/Written Through 2-Wire Serial Interface (SDA and SCL Pins) Data Lines Filtered Internally for Noise Immunity (50ns Deglitch) Bus Timeout Feature Prevents Lockup Problems on 2-Wire Interface Multidrop Capability Simplifies Distributed Temperature-Sensing Applications Pin/Software Compatible with the LM75 Available in 8-Pin μSOP (μMAX®) and SO Packages APPLICATIONS Any Thermally Sensitive System Cellular Base Stations Telecom Switches and Routers Servers PIN CONFIGURATIONS ORDERING INFORMATION PART SDA 1 2 O.S. 3 GND 4 DS75 LX SCL 8 VDD 7 A0 6 A1 5 A2 SO (150 mils) 1 SCL 2 O.S. GND 3 4 DS75 LX SDA TEMP RANGE DS75LXS+ -55°C to +125°C DS75LXS+T&R -55°C to +125°C DS75LXU+ -55°C to +125°C DS75LXU+T&R -55°C to +125°C PIN PACKAGE 8 SO (150 mils) 8 SO (150 mils), 2500 Piece 8 µSOP (µMAX) 8 µSOP (µMAX), 3000 Piece + Denotes lead-free package. T&R denotes tape-and-reel. 8 VDD 7 A0 6 A1 Note: A “+” symbol will also be marked on the package near the pin 1 indicator. 5 A2 µMAX is a registered trademark of Maxim Integrated Products, Inc. μSOP/μMAX 1 of 13 050307 DS1386/DS1386P ABSOLUTE MAXIMUM RATINGS Voltage Range on VDD, Relative to Ground Voltage Range on Any Other Pin, Relative to Ground Operating Temperature Range Storage Temperature Range Soldering Temperature -0.3V to +4.0V -0.3V to +6.0V -55°C to +125°C -55°C to +125°C See IPC/JEDEC J-STD-020 These are stress ratings 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. The Dallas Semiconductor DS75LX is built to the highest quality standards and manufactured for long-term reliability. All Dallas Semiconductor devices are made using the same quality materials and manufacturing methods. However, the DS75LX is not exposed to environmental stresses, such as burn-in, that some industrial applications require. For specific reliability information on this product, contact the factory in Dallas at (972) 3714448. DC ELECTRICAL CHARACTERISTICS (1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.) PARAMETER SYMBOL Supply Voltage VDD Thermometer Error TERR (Note 2) Input Logic-High SDA, VIH SCL Input Logic-Low SDA, VIL SCL VOL1 SDA Output Logic-Low Voltage (Note 3) VOL2 O.S. Saturation Voltage Input Current SDA, SCL I/O Capacitance Address Input Sink Current Address Input Source Current Address Voltage High Address Voltage Low Standby Current Active Current (Notes 1, 4, 5) VOL CONDITIONS (Note 1) -25°C to +100°C -55°C to +125°C (Note 3) MIN 1.7 MAX 3.7 ±2.0 ±3.0 UNITS V 0.7 x VDD VDD + 0.3 V VSS - 0.3 0.3 x VDD V 0 0 0.4 0.6 V 0.8 V -10 +10 10 µA pF 0.2 3.5 µA 0.2 3.5 µA 3mA sink current 6mA sink current 4mA sink current (Notes 2, 3) 0.4 < VI/O < 0.9VDD CI/O ILAH ILAL VAH VAL IDD1 IDD A0, A1, or A2 tied to VDD (Notes 4, 5) A0, A1, or A2 tied to GND (Notes 4, 5) (Note 6) (Note 6) (Notes 4, 5) Active temp conversions Communication only VDD - .04 VSS + .04 13 1000 100 °C V V µA µA AC ELECTRICAL CHARACTERISTICS (1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.) PARAMETER SYMBOL Resolution Temperature Conversion Time CONDITIONS MIN 9 TYP MAX 12 9-bit conversions 25 10-bit conversions 50 11-bit conversions 100 12-bit conversions 200 UNITS Bits ms tCONVT 2 of 13 SCL Frequency fSCL DS75LX: Digital Thermometer and Thermostat with Extended Addressing 400 kHz AC ELECTRICAL CHARACTERISTICS (continued) (1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C.) PARAMETER SYMBOL Bus Free Time Between tBUF a STOP and START Condition START and Repeated tHD:STA START Hold Time from Falling SCL Low Period of SCL tLOW High Period of SCL tHIGH Repeated START tSU:STA Condition Setup Time to Rising SCL Data-Out Hold Time from tHD:DAT Falling SCL Data-In Setup Time to tSU:DAT Rising SCL Rise Time of SDA and tR SCL (Receive) Fall Time of SDA and tF SCL (Receive) Spike Suppression tSS Filter Time (Deglitch Filter) STOP Setup Time to tSU:STO Rising SCL Capacitive Load for Each CB Bus Line Input Capacitance CI Serial Interface Reset tTIMEOUT Time CONDITIONS MIN TYP 1.3 (Note 7) (Notes 7, 8) Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: UNITS µs 600 ns (Note 7) (Note 7) 1.3 0.6 µs µs (Note 7) 600 ns (Notes 7, 9) 0 0.9 100 (Note 7) (Notes 7, 10) µs ns 20 + 0.1CB 20 + 0.1CB 300 ns 300 ns 50 ns B (Notes 7, 10) B 0 (Note 7) 600 ns 400 B Note 1: MAX 5 SDA time low (Notes 11, 12) 75 pF pF 325 ms VDD must be decoupled with a high-quality 0.1µF bypass capacitor. X5R or X7R ceramic surface-mount capacitors are recommended. Internal heating caused by O.S. loading causes the DS75LX to read approximately 0.5°C higher if O.S. is sinking the max rated current. All voltages are referenced to ground. IDD specified with O.S. pin open and A0–A2 pins grounded. IDD and address leakage specified with VDD at 3.0V and SDA, SCL = 3.0V at 0°C to +70°C. Address pins A0, A1, A2 are directly connected to VDD, VSS, or floating with less than 50pF capacitive load. See the timing diagram (Figure 1). All timing is referenced to 0.9 x VDD and 0.1 x VDD. After this period, the first clock pulse is generated. The DS75LX provides an internal hold time of at least 75ns on the SDA signal to bridge the undefined region of SCL's falling edge. For example, if CB = 300pF, then tR[min] = tF[min] = 50ns. This timeout applies only when the DS75LX is holding SDA low. Other devices can hold SDA low indefinitely and the DS75LX will not reset. The DS75LX is available with timeout feature disabled upon special order. Contact Factory. PIN DESCRIPTION PIN 1 2 3 4 5 6 7 NAME SDA SCL O.S. GND A2 A1 A0 8 VDD FUNCTION Data Input/Output for 2-Wire Serial Communication Port (Open Drain) Clock Input for 2-Wire Serial Communication Port Thermostat Output Open Drain Ground Address Input Address Input Address Input Supply Voltage. +1.7V to +3.7V supply pin. VDD must have an external bypass capacitor to GND. 0.1µF X5R or X7R ceramic SMT caps recommended. 3 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing BLOCK DIAGRAM PRECISION REFERENCE OVERSAMPLING MODULATOR DIGITAL DECIMATOR VDD SCL SDA A0 A1 A2 CONFIGURATION REGISTER ADDRESS AND I/O CONTROL TEMPERATURE REGISTER RP O.S. TOS AND THYST REGISTERS GND Figure 1. Timing Diagram 4 of 13 THERMOSTAT COMPARATOR DS75LX: Digital Thermometer and Thermostat with Extended Addressing OPERATION—MEASURING TEMPERATURE The DS75LX measures temperature using a bandgap temperature-sensing architecture. An on-board delta-sigma analog-to-digital converter (ADC) converts the measured temperature to a digital value that is calibrated in degrees celsius; for Fahrenheit applications a lookup table or conversion routine must be used. The DS75LX is factorycalibrated and requires no external components to measure temperature. At power-up the DS75LX immediately begins measuring and converting its own temperature to a digital value. The resolution of the digital output data is user-configurable to 9, 10, 11, or 12 bits, corresponding to temperature increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively, with 9-bit default resolution at power-up. The resolution is controlled via the R0 and R1 bits in the configuration register as explained in the Configuration Register section of this data sheet. Note that the conversion time doubles for each additional bit of resolution. After each temperature measurement and analog-to-digital conversion, the DS75LX stores the temperature as a 16-bit two’s complement number in the 2-byte temperature register (see Figure 2). The sign bit (S) indicates if the temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The most recently converted digital measurement can be read from the temperature register at any time. Since temperature conversions are performed in the background, reading the temperature register does not affect the operation in progress. Bits 3 through 0 of the temperature register are hardwired to 0. When the DS75LX is configured for 12-bit resolution, the 12 MSbs (bits 15 through 4) of the temperature register contain temperature data. For 11-bit resolution, the 11 MSbs (bits 15 through 5) of the temperature register contain data, and bit 4 reads out as 0. Likewise, for 10-bit resolution, the 10 MSbs (bits 15 through 6) contain data, and for 9-bit the 9 MSbs (bits 15 through 7) contain data, and all unused LSbs will contain 0s. Table 1 gives examples of 12-bit resolution digital output data and the corresponding temperatures. Figure 2. Temperature, TH, and TL Register Format MS Byte bit 15 S bit 14 26 bit 13 25 bit 12 24 bit 11 23 bit 10 22 bit 9 21 bit 8 20 LS Byte bit 7 2-1 bit 6 2-2 bit 5 2-3 bit 4 2-4 bit 3 0 bit 2 0 bit 1 0 bit 0 0 Table 1. 12-Bit Resolution Temperature/Data Relationship TEMPERATURE (°C) DIGITAL OUTPUT (BINARY) DIGITAL OUTPUT (HEX) +125 0111 1101 0000 0000 7D00h +25.0625 0001 1001 0001 0000 1910h +10.125 0000 1010 0010 0000 0A20h +0.5 0000 0000 1000 0000 0080h 0 0000 0000 0000 0000 0000h -0.5 1111 1111 1000 0000 FF80h -10.125 1111 0101 1110 0000 F5E0h -25.0625 1110 0110 1111 0000 E6F0h -55 1100 1001 0000 0000 C900h 5 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Shutdown Mode For power-sensitive applications, the DS75LX offers a low-power shutdown mode. The SD bit in the configuration register controls shutdown mode. When SD is changed to 1, the conversion in progress is completed and the result is stored in the temperature register after which the DS75LX goes into a low-power standby state. The O.S. output is cleared if the thermostat is operating in interrupt mode, and O.S remains unchanged in comparator mode. The 2wire interface remains operational in shutdown mode, and writing a 0 to the SD bit returns the DS75LX to normal operation. OPERATION—THERMOSTAT The DS75LX thermostat has two operating modes, comparator mode and interrupt mode, which activate and deactivate the open-drain thermostat output (O.S.) based on user-programmable trip-points (TOS and THYST). The DS75LX powers up with the thermostat in comparator mode with active-low O.S. polarity and with the overtemperature trip-point (TOS) register set to +80°C and the hysteresis trip-point (THYST) register set to +75°C. If these power-up settings are compatible with the application, the DS75LX can be used as a stand-alone thermostat (i.e., no 2-wire communication required). If interrupt mode operation, active-high O.S. polarity, or different TOS and THYST values are desired, they must be programmed after power-up, so stand-alone operation is not possible. In both operating modes, the user can program the thermostat fault tolerance, which sets how many consecutive temperature readings (1, 2, 4, or 6) must fall outside of the thermostat limits before the thermostat output is triggered. The fault tolerance is set by the F1 and F0 bits in the configuration register and at power-up the fault tolerance is 1. The data format of the TOS and THYST registers is identical to that of the temperature register (see Figure 2), i.e., a 2-byte two’s complement representation of the trip-point temperature in degrees celcius with bits 3 through 0 hardwired to 0. After every temperature conversion, the measured temperature is compared to the values in the TOS and THYST registers, and then O.S. is updated based on the result of the comparison and the operating mode. The number of TOS and THYST bits used during the thermostat comparison is equal to the conversion resolution set by the R1 and R0 bits in the configuration register. For example, if the resolution is 9 bits, only the 9 MSbs of TOS and THYST will be used by the thermostat comparator. The active state of the O.S. output can be changed by the POL bit in the configuration register. The power-up default is active low. If the user does not wish to use the thermostat capabilities of the DS75LX, the O.S. output should be left floating. Note that if the thermostat is not used, the TOS and THYST registers can be used for general storage of system data. Comparator Mode When the thermostat is in comparator mode, O.S. can be programmed to operate with any amount of hysteresis. The O.S. output becomes active when the measured temperature exceeds the TOS value a consecutive number of times as defined by the F1 and F0 fault tolerance (FT) bits in the configuration register. O.S. then stays active until the first time the temperature falls below the value stored in THYST. Putting the device into shutdown mode does not clear O.S. in comparator mode. Thermostat comparator mode operation with FT = 2 is illustrated in Figure 3. Interrupt Mode In interrupt mode, the O.S. output first becomes active when the measured temperature exceeds the TOS value a consecutive number of times equal to the FT value in the configuration register. Once activated, O.S. can only be cleared by either putting the DS75LX into shutdown mode or by reading from any register (temperature, configuration, TOS, or THYST ) on the device. Once O.S. has been deactivated, it will only be reactivated when the measured temperature falls below the THYST value a consecutive number of times equal to the FT value. Again, O.S can only be cleared by putting the device into shutdown mode or reading any register. Thus, this interrupt/clear process is cyclical between TOS and THYST events (i.e, TOS, clear, THYST, clear, TOS, clear, THYST, clear, etc.). Thermostat interrupt mode operation with FT = 2 is illustrated in Figure 3. 6 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Figure 3. O.S. Output Operation Example In this example the DS75LX is configured to have a fault tolerance of 2. TOS Temperature THYST Inactive O.S. Output - Comparator Mode Active Inactive O.S. Output - Interrupt Mode Active Assumes an interrupt clear event has occurred Conversions Configuration Register The configuration register allows the user to program various DS75LX options such as conversion resolution, thermostat fault tolerance, thermostat polarity, thermostat operating mode, and shutdown mode. The configuration register is arranged as shown in Figure 4 and detailed descriptions of each bit are provided in Table 2. The user has read/write access to all bits in the configuration register except the MSb, which is a reserved read-only bit. The entire register is volatile, and thus powers up in its default state. Figure 4. Configuration Register MSb bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 LSb 0 R1 R0 F1 F0 POL TM SD 7 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Table 2. Configuration Register Bit Descriptions BIT NAME 0 Reserved R1 Conversion Resolution Bit 1 R0 Conversion Resolution Bit 0 F1 Thermostat Fault Tolerance Bit 1 F0 Thermostat Fault Tolerance Bit 0 POL Thermostat Output (O.S.) Polarity TM Thermostat Operating Mode SD Shutdown DESCRIPTION Power-Up State = 0 The master can write to this bit, but it always reads out as a 0. Power-Up State = 0 Sets conversion resolution (see Table 3). Power-Up State = 0 Sets conversion resolution (see Table 3). Power-Up State = 0 Sets the thermostat fault tolerance (see Table 4). Power-Up State = 0 Sets the thermostat fault tolerance (see Table 4). Power-Up State = 0 POL = 0 — O.S. is active low. POL = 1 — O.S. is active high. Power-Up State = 0 TM = 0 — Comparator mode. TM = 1 — Interrupt mode. See the Operation—Thermostat section for a detailed description of these modes. Power-Up State = 0 SD = 0 — Active conversion and thermostat operation. SD = 1 — Shutdown mode. See the Shutdown Mode section for a detailed description of this mode. Table 3. Resolution Configuration R1 R0 0 0 1 1 0 1 0 1 THERMOMETER RESOLUTION (BITS) 9 10 11 12 MAX CONVERSION TIME (ms) 25 50 100 200 Table 4. Fault Tolerance Configuration F1 F0 0 0 1 1 0 1 0 1 CONSECUTIVE OUT-OF-LIMITS CONVERSIONS TO TRIGGER O.S. 1 2 4 6 REGISTER POINTER The four DS75LX registers each have a unique two-bit pointer designation, which is defined in Table 5. When reading from or writing to the DS75LX, the user must “point” the DS75LX to the register that is to be accessed. When reading from the DS75LX, once the pointer is set it remains pointed at the same register until it is changed. For example, if the user wants to perform consecutive reads from the temperature register, the pointer only has to be set to the temperature register one time, after which all reads will automatically be from the temperature register until the pointer value is changed. On the other hand, when writing to the DS75LX, the pointer value must be refreshed each time a write is performed, even if the same register is being written to twice in a row. At power-up, the default pointer value is the temperature register so the temperature register can be read immediately without resetting the pointer. Changes to the pointer setting are accomplished as described in the 2-Wire Serial Data Bus. 8 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Table 5. Pointer Definition REGISTER Temperature Configuration THYST TOS P1 0 0 1 1 P0 0 1 0 1 2-WIRE SERIAL DATA BUS The DS75LX communicates over a standard bidirectional, 2-wire serial data bus that consists of a serial clock (SCL) signal and serial data (SDA) signal. The DS75LX interfaces to the bus through the SCL input pin and opendrain SDA I/O pin. All communication is MSb first. The following terminology is used to describe 2-wire communication: Master Device: Microprocessor/microcontroller that controls the slave devices on the bus. The master device generates the SCL signal and START and STOP conditions. Slave: All devices on the bus other than the master. The DS75LX always functions as a slave. Bus Idle or Not Busy: Both SDA and SCL remain high. SDA is held high by a pullup resistor when the bus is idle, and SCL must either be forced high by the master (if the SCL output is push-pull) or pulled high by a pullup resistor (if the SCL output is open drain). Transmitter: A device (master or slave) that is sending data on the bus. Receiver: A device (master or slave) that is receiving data from the bus. START Condition: Signal generated by the master to indicate the beginning of a data transfer on the bus. The master generates a START condition by pulling SDA from high to low while SCL is high (see Figure 5). A “repeated” START is sometimes used at the end of a data transfer (instead of a STOP) to indicate that the master will perform another operation. STOP Condition: Signal generated by the master to indicate the end of a data transfer on the bus. The master generates a STOP condition by transitioning SDA from low to high while SCL is high (see Figure 5). After the STOP is issued, the master releases the bus to its idle state. Acknowledge (ACK): When a device (either master or slave) is acting as a receiver, it must generate an acknowledge (ACK) on the SDA line after receiving every byte of data. The receiving device performs an ACK by pulling the SDA line low for an entire SCL period (see Figure 5). During the ACK clock cycle, the transmitting device must release SDA. A variation on the ACK signal is the “not acknowledge” (NACK). When the master device is acting as a receiver, it uses a NACK instead of an ACK after the last data byte to indicate that it is finished receiving data. The master indicates a NACK by leaving the SDA line high during the ACK clock cycle. Slave Address: Every slave device on the bus has a unique 7-bit address that allows the master to access that device. The DS75LX’s 7-bit bus address depends on the state of the external address pins A0–A2. See Table 6. The three address pins allow up to 27 DS75LXs to be multidropped on the same bus. When tying an address line high or low, connect the address line directly to VDD or GND. Do not use series resistors on these pins. Address Byte: The address byte is transmitted by the master and consists of the 7-bit slave address plus a read/write (R/W ¯¯) bit (see Figure 6). If the master is going to read data from the slave device then R/W ¯¯ = 1, and if the master is going to write data to the slave device then R/W ¯¯ = 0. Pointer Byte: The pointer byte is used by the master to tell the DS75LX which register is going to be accessed during communication. The six MSbs of the pointer byte (see Figure 7) are always 0 and the two LSbs correspond to the desired register as shown in Table 6. 9 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Figure 5. Start, Stop, and ACK Signals SDA … SCL … ACK (or NACK) STOP From Receiver Condition START Condition Figure 6. Address Byte BIT 7 a6 BIT 6 a5 BIT 5 a4 BIT 4 a3 BIT 3 a2 BIT 2 a1 BIT 1 a0 BIT 0 R/W ¯¯ The Address Pins A0–A2 are tri-state inputs. These can be low, high, or floating in any combination, resulting in 27 address possibilities. These map into the address byte according to Table 6. Figure 7. Pointer Byte BIT 7 0 BIT 6 0 BIT 5 0 BIT 4 0 BIT 3 0 BIT 2 0 BIT 1 P1 BIT 0 P0 GENERAL 2-WIRE INFORMATION All data is transmitted MSb first over the 2-wire bus. One bit of data is transmitted on the 2-wire bus each SCL period. A pullup resistor is required on the SDA line and, when the bus is idle, both SDA and SCL must remain in a logic-high state. All bus communication must be initiated with a START condition and terminated with a STOP condition. During a START or STOP is the only time SDA is allowed to change states while SCL is high. At all other times, changes on the SDA line can only occur when SCL is low: SDA must remain stable when SCL is high. After every 8-bit (1-byte) transfer, the receiving device must answer with an ACK (or NACK), which takes one SCL period. Therefore, nine clocks are required for every 1-byte data transfer. 10 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Table 6. Address Configuration A2 A1 A0 ADDRESS 0 0 0 1001000 0 0 1 1001001 0 1 0 1001010 0 1 1 1001011 0 0 FLOAT 0101100 0 FLOAT 0 0101000 0 1 FLOAT 0101101 0 FLOAT 1 0101001 0 FLOAT FLOAT 0110101 1 0 0 1001100 1 0 1 1001101 1 1 0 1001110 1 1 1 1001111 1 0 FLOAT 0101110 1 FLOAT 0 0101010 1 1 FLOAT 0101111 1 FLOAT 1 0101011 1 FLOAT FLOAT 0110110 FLOAT 0 0 1110000 FLOAT 0 1 1110010 FLOAT 1 0 1110011 FLOAT 1 1 1110101 FLOAT 0 FLOAT 1110001 FLOAT FLOAT 0 1110110 FLOAT 1 FLOAT 1110100 FLOAT FLOAT 1 1110111 FLOAT FLOAT FLOAT 0110111 11 of 13 DS75LX: Digital Thermometer and Thermostat with Extended Addressing Writing to the DS75LX To write to the DS75LX, the master must generate a START followed by an address byte containing the DS75LX bus address. The value of the R/W ¯¯ bit must be a 0, which indicates that a write is about to take place. The DS75LX responds with an ACK after receiving the address byte. This must be followed by a pointer byte from the master, which tells the DS75LX which register is being written to. The DS75LX again responds with an ACK after receiving the pointer byte. Following this ACK the master device must immediately begin transmitting data to the DS75LX. When writing to the configuration register, the master must send one byte of data (see Figure 8a), and when writing to the TOS or THYST registers the master must send two bytes of data (see Figure 8b). After receiving each data byte, the DS75LX responds with an ACK, and the transaction is finished with a STOP from the master. Software POR The soft POR command is hex 54. Issue a write command to the DS75LX. It responds with an ACK. If the next byte is a 0x54, the DS75LX will reset as if power had been cycled. No ACK is sent by the IC after the POR command is received. Reading from the DS75LX When reading from the DS75LX, if the pointer was already pointed to the desired register during a previous transaction, the read can be performed immediately without changing the pointer setting. In this case the master sends a START followed by an address byte containing the DS75LX bus address. The R/W ¯¯ bit must be a 1, which tells the DS75LX that a read is being performed. After the DS75LX sends an ACK in response to the address byte, the DS75LX begins transmitting the requested data on the next clock cycle. When reading from the configuration register, the DS75LX transmits one byte of data, after which the master must respond with a NACK followed by a STOP (see Figure 8c). For 2-byte reads (i.e., from the temperature, TOS, or THYST register), the DS75LX transmits two bytes of data, and the master must respond to the first data byte with an ACK and to the second byte with a NACK followed by a STOP (see Figure 8d). If only the most significant byte of data is needed, the master can issue a NACK followed by a STOP after reading the first data byte, in which case the transaction will be the same as for a read from the configuration register. If the pointer is not already pointing to the desired register, the pointer must first be updated as shown in Figure 8e, which shows a pointer update followed by a single-byte read. The value of the R/W ¯¯ bit in the initial address byte is a 0 (“write”) since the master is going to write a pointer byte to the DS75LX. After the DS75LX responds to the address byte with an ACK, the master sends a pointer byte that corresponds to the desired register. The master must then perform a repeated START followed by a standard 1- or 2-byte read sequence (with R/W ¯¯ = 1) as described in the previous paragraph. PACKAGE INFORMATION (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.) PACKAGE 8-Pin SO 8-Pin µSOP/µMAX DOCUMENT NO. 56-G2008-001 21-0036 12 of 13 1 START S 1 0 0 1 Address Byte 1 0 A 1 1 0 0 1 Address Byte 1 0 A SCL 1 13 of 13 1 0 0 1 Address Byte 1 0 A 0 ACK (DS75LX) W 0 0 1 START S 1 0 0 1 Address Byte 1 0 A 0 ACK (DS75LX) W 0 0 0 0 0 0 0 Pointer Byte 0 0 Pointer Byte 0 Pointer Byte 0 0 0 A S 1 SCL 1 START S 1 0 0 1 Address Byte 1 0 A Data Byte (from DS75LX) P NACK STOP (Master) D7 D6 D5 D4 D3 D2 D1 D0 N ACK (DS75LX) R 0 0 1 Address Byte 1 An address byte value of 1110010 corresponds to A0 connected to VDD, A1 connected to GND, and A2 floating. SDA 1 ACK Repeat (DS75LX ) START P1 P0 A MS Data Byte (from Master) P 0 A Data Byte (from DS75LX) P NACK STOP (Master) P ACK STOP (DS75LX) D7 D6 D5 D4 D3 D2 D1 D0 N ACK (DS75LX) R LS Data Byte (from Master) D7 D6 D5 D4 D3 D2 D1 D0 A ACK (DS75LX) A ACK STOP (DS75LX) D7 D6 D5 D4 D3 D2 D1 D0 ACK (DS75LX) A Data Byte (from Master) P NACK STOP (Master) D7 D6 D5 D4 D3 D2 D1 D0 A ACK (DS75LX) 1 P1 P0 0 LS Data Byte (from DS75LX) D7 D6 D5 D4 D3 D2 D1 D0 N ACK (Master) A e) Read From the Configuration Register (current pointer location) on) SDA SCL d) Read Single Byte (new pointer location) START SDA S 0 ACK (DS75LX) W c) Write to the TOS or T HYST Register START SDA S SCL MS Data Byte (from DS75LX) D7 D6 D5 D4 D3 D2 D1 D0 ACK (DS75LX) R b) Write to the Configuration Register SDA SCL a) Read 2-Bytes Bytes From the Temperature, TOS or THYST Register (current pointer location) DS75LX: Digital Thermometer and Thermostat with Extended Addressing Figure 8. 2-Wire Interface Timing