MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor General Description The MAX31820PAR ambient temperature sensor provides 9-bit to 12-bit Celsius temperature measurements with 0.5C accuracy over a +10C to +45C temperature range. Over its entire -55C to +125C operating range, the device has 2.0C accuracy. The device communicates over a 1-Wire(R) bus that, by definition, requires only one data line (and ground) for communication with a central microprocessor. In addition, the device derives power directly from the data line ("parasite power"), eliminating the need for an external power supply. Requiring so few pins enables the device to be placed in a 3-pin TO-92 package. The form factor of this package allows the device to be placed above the board and thus measure the ambient temperature of a system, as opposed to the board temperature that a surface-mount package would measure. Each MAX31820PAR has a unique 64-bit serial code, which allows multiple MAX31820PAR devices to function on the same 1-Wire bus. Therefore, it is simple to use one microprocessor to control many devices distributed over a large area. Applications HVAC Environmental Controls Temperature Monitoring Systems Inside Buildings, Equipment, or Machinery Process Monitoring and Control Systems Thermostatic Controls Industrial Systems Consumer Products Thermometers Any Thermally Sensitive System Block Diagram Benefits and Features Unique 1-Wire Interface Requires Only One Port Pin for Communication Derives Power from Data Line (Parasite Power); No Local Power Supply Needed Multidrop Capability Simplifies Distributed Temperature-Sensing Applications Requires No External Components Measures Temperatures from -55C to +125C (-67F to +257F) 0.5C Accuracy from +10C to +45C Thermometer Resolution is User-Selectable from 9 Bits to 12 Bits Converts Temperature to 12-Bit Digital Word in 750ms (Max) User-Definable Nonvolatile (NV) Alarm Settings Alarm Search Command Identifies and Addresses Devices Whose Temperature is Outside Programmed Limits (Temperature Alarm Condition) Available in 3-Pin TO-92 Package Software Compatible with the DS1822-PAR and DS18B20-PAR Ordering Information appears at end of data sheet. For related parts and recommended products to use with this part, refer to www.maximintegrated.com/MAX31820PAR.related. VPU MEMORY CONTROL LOGIC PARASITE-POWER CIRCUIT 4.7k MAX31820PAR DQ CPP TEMPERATURE REGISTER 64-BIT ROM AND 1-Wire PORT ALARM HIGH TRIGGER (TH) REGISTER (EEPROM) SCRATCHPAD GND ALARM LOW TRIGGER (TL) REGISTER (EEPROM) CONFIGURATION REGISTER (EEPROM) 8-BIT CRC GENERATOR 1-Wire is a registered trademark of Maxim Integrated Products, Inc. 19-6732; Rev 0; 6/13 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Absolute Maximum Ratings Voltage Range on Any Pin Relative to Ground.....-0.5V to +6.0V Operating Temperature Range.......................... -55C to +100C Storage Temperature Range............................. -55C to +125C Soldering Temperature (reflow)........................................+260C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. DC Electrical Characteristics (VPU = 3.0V to 3.7V, TA = -55C to +100C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL Pullup Supply Voltage VPU Thermometer Error TERR CONDITIONS (Notes 2, 3) MIN TYP 3.0 MAX UNITS 3.7 V +10C to +45C 0.5 -55C to +100C 2 Input Logic-Low VIL (Notes 2, 4, 5) -0.3 +0.8 Input Logic-High VIH (Notes 2, 6) 3.0 3.7 VI/O = 0.4V (Note 2) 4.0 Sink Current IL C V V mA Active Current IDQA (Note 7) 1 DQ Input Current IDQ (Note 8) 5 A (Note 9) 0.2 C Drift www.maximintegrated.com 1.5 mA Maxim Integrated 2 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor AC Electrical Characteristics (VPU = 3.0V to 3.7V, TA = -55C to +100C, unless otherwise noted.) (Note 1) PARAMETER Temperature Conversion Time SYMBOL tCONV CONDITIONS TYP MAX UNITS 93.75 10-bit resolution 187.5 11-bit resolution 375 12-bit resolution 750 10 s 120 s Time to Strong Pullup On tSPON Start Convert T command or Copy Scratchpad command issued Time Slot tSLOT (Note 10) Recovery Time MIN 9-bit resolution 60 ms tREC (Note 10) 1 Write-Zero Low Time tLOW0 (Note 10) 60 120 s Write-One Low Time 1 15 s 15 s tLOW1 (Note 10) Read Data Valid tRDV (Note 10) Reset Time High tRSTH (Note 10) 480 tRSTL Reset Time Low s s (Notes 10, 11) 480 960 s tPDHIGH (Note 10) 15 60 s Presence-Detect Low tPDLOW (Note 10) 60 240 s Capacitance CIN/OUT 25 pF Presence-Detect High NONVOLATILE MEMORY Nonvolatile Write Cycle Time EEPROM Writes EEPROM Data Retention tWR 2 10 ms NEEWR -55C to +55C 50k Writes tEEDR -55C to +55C 10 Years Note 1: Limits are 100% tested at TA = +25C and TA = +85C. Limits over the operating temperature range and relevant supply voltage are guaranteed by design and characterization. Note 2: All voltages are referenced to ground. Note 3: The pullup supply voltage specification assumes that the pullup device (resistor or transistor) is ideal, and therefore the high level of the pullup is equal to VPU. In order to meet the device's VIH spec, the actual supply rail for the strong pullup transistor must include margin for the voltage drop across the transistor when it is turned on; thus: VPU_ACTUAL = VPU_ IDEAL + VTRANSISTOR. Note 4: Logic-low voltages are specified at a sink current of 4mA. Note 5: To guarantee a presence pulse under low-voltage parasite-power conditions, VILMAX may have to be reduced to as low as 0.5V. Note 6: Logic-high voltages are specified at a source current of 1mA. Note 7: Active current refers to supply current during active temperature conversions or EEPROM writes. Note 8: DQ line is high (high-Z state). Note 9: Drift data is based on a 1000-hour stress test at +125C. Note 10: See the 1-Wire Timing Diagrams. Note 11: If tRSTL > 960s, a power-on reset may occur. www.maximintegrated.com Maxim Integrated 3 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor 1-Wire Timing Diagrams 1-Wire WRITE-ZERO TIME SLOT START OF NEXT CYCLE tSLOT tREC tLOW0 1-Wire READ-ZERO TIME SLOT tSLOT tREC START OF NEXT CYCLE tRDV 1-Wire RESET PULSE RESET PULSE FROM HOST tRSTL tRSTH 1-Wire PRESENCE DETECT PRESENCE DETECT tPDHIGH tPDLOW www.maximintegrated.com Maxim Integrated 4 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Pin Configuration SIDE VIEW FRONT VIEW GND 1 1 DQ 2 2 N.C. 3 3 MAX31820PAR TO-92 Pin Description PIN NAME 1 GND FUNCTION 2 DQ Data Input/Output. Open-drain, 1-Wire interface pin that provides power to the device when used in parasite power mode (see the Parasite Power section). 3 N.C. Not Connected. Does not connect to internal circuit. Ground Detailed Description The MAX31820PAR ambient temperature sensor provides 9-bit to 12-bit Celsius temperature measurements with 0.5C accuracy over a +10C to +45C temperature range. Over its entire -55C to +125C operating range, the device has 2.0C accuracy. The device communicates over a 1-Wire bus that, by definition, requires only one data line (and ground) for communication with a central microprocessor. In addition, the device derives power directly from the data line ("parasite power"), eliminating the need for an external power supply. Requiring so few pins enables the device to be placed in a 3-pin TO-92 package. The form factor of this package allows the device to be placed above the board and thus measure the ambient temperature of a system, as opposed to the board temperature that a surface-mount package would measure. Each device has a unique 64-bit serial code, allowing multiple MAX31820PAR devices to function on the same 1-Wire bus. Therefore, it is simple to use one microprocessor to control many devices distributed over a large area. The 64-bit ROM stores the device's unique serial code. The scratchpad memory contains the 2-byte temperature register that stores the digital output from the temperature sensor. In addition, the scratchpad provides access to the 1-byte upper and lower alarm trigger www.maximintegrated.com registers (TH and TL) and the 1-byte configuration register. The configuration register allows the user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. The TH, TL, and configuration registers are nonvolatile (EEPROM), so they retain data when the device is powered down. The device uses Maxim Integrated's 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 through a three-state or open-drain port (i.e., the MAX31820PAR's DQ pin). In this bus system, the microprocessor (the master device) identifies and addresses devices on the bus using each device's unique 64-bit code. Because 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 section. The device can also operate without an external power supply. Power is instead supplied through the 1-Wire pullup resistor through the DQ pin when the bus is high. The high bus signal also charges an internal capacitor (CPP), which then supplies power to the device when the bus is low. This method of deriving power from the 1-Wire bus is referred to as "parasite power." Maxim Integrated 5 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Operation other components to the sensor. As much as practical, avoid copper in the vicinity of the sensor. Measuring Ambient Temperature The device's core functionality is its direct-to-digital temperature sensor. The resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5C, 0.25C, 0.125C, and 0.0625C, respectively. The default resolution at power-up is 12 bits. The device powers up in a low-power 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 temperature register in the scratchpad memory and the device returns to its idle state. A conventional surface-mount temperature sensor IC has an excellent thermal connection to the circuit board on which it is mounted. Heat travels from the board through the leads to the sensor die. Air temperature can affect the die temperature, but the sensor's package does not conduct heat as well as the leads, so board temperature has the greatest influence on the measured temperature. The device's TO-92 package allows the sensor die to be positioned above the board. The leads still conduct some heat from the board, but because there is significant lead area in contact with air, their temperature is also strongly affected by air temperature. Follow the guidelines below to get the best results when measuring ambient temperature: * If air is moving (e.g., due to cooling fans), place the sensor in the path of the air stream. This causes the ambient temperature to influence the sensor temperature more strongly. * If the board contains components that will heat it, mount the sensor as far as possible from those components. This makes the temperature in the vicinity of the sensor closer to the temperature of the ambient air. * PCB traces and ground planes conduct heat from The output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, a lookup table 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 the Temperature Register Format). The sign bits (S) indicate if the temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the device is configured for 12-bit resolution, all bits in the temperature register contain valid data. For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and the corresponding temperature reading for 12-bit resolution conversions. Temperature Register Format BIT 15 MSB LSB BIT 14 BIT 13 BIT 12 BIT 11 BIT 10 BIT 9 BIT 8 25 24 S S S S S 26 BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 23 22 21 20 2-1 2-2 2-3 2-4 Table 1. Temperature/Data Relationship TEMPERATURE (C) DIGITAL OUTPUT (BINARY) +85* 0000 0101 0101 0000 DIGITAL OUTPUT (HEX) 0550h +25.0625 0000 0001 1001 0001 0191h +10.125 0000 0000 1010 0010 00A2h +0.5 0000 0000 0000 1000 0008h 0 0000 0000 0000 0000 0000h -0.5 1111 1111 1111 1000 FFF8h -10.125 1111 1111 0101 1110 FF5Eh -25.0625 1111 1110 0110 1111 FE6Fh -55 1111 1100 1001 0000 FC90h *The power-on-reset value of the temperature register is +85C. www.maximintegrated.com Maxim Integrated 6 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Alarm Signaling After the device performs a temperature conversion, the temperature value is compared to the user-defined two's complement alarm trigger values stored in the 1-byte TH and TL registers (see TH and TL Register Format). The sign bit (S) indicates if the value is positive or negative; for positive numbers S = 0 and for negative numbers S = 1. The TH and TL registers are nonvolatile (EEPROM) so they retain data when the device is powered down. TH and TL can be accessed through bytes 2 and 3 of the scratchpad, as explained in the Memory section. Only bits 11:4 of the temperature register are used in the TH and TL comparison since TH and TL are 8-bit registers. If the measured temperature is lower than or equal to TL or higher than or equal to TH, an alarm condition exists and an alarm flag is set inside the device. This flag is updated after every temperature measurement; therefore, if the alarm condition goes away, the flag is turned off after the next temperature conversion. The master device can check the alarm flag status of all MAX31820PAR devices on the bus by issuing an Alarm Search [ECh] command. Any devices with a set alarm flag respond to the command, so the master can determine exactly which devices have experienced an alarm condition. If an alarm condition exists and the TH or TL settings have changed, another temperature conversion should be done to validate the alarm condition. Parasite Power The device's parasite-power circuit allows it to operate without a local power supply. Parasite power is very useful for applications that require remote temperature sensing, or those that are very space constrained. Figure 1 shows the device's parasite-power control circuitry, which "steals" power from the 1-Wire bus through the DQ pin when the bus is high. The stolen charge powers the device while the bus is high, and some of the charge is stored on the parasite-power capacitor (CPP) to provide power when the bus is low. In parasite-power mode, the 1-Wire bus and CPP can provide sufficient current to the device for most operations as long as the specified timing and voltage requirements are met (see the DC Electrical Characteristics and AC Electrical Characteristics tables). However, when the device is performing temperature conversions or copying data from the scratchpad memory to EEPROM, the operating current can be as high as 1.5mA. This current can cause an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be supplied by CPP. To ensure that the device has sufficient supply current, it is necessary to provide a strong pullup on the 1-Wire bus whenever temperature 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 TH and TL Register Format BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 S 26 25 24 23 22 21 20 VPU MAX31820PAR VPU P GND DQ 4.7k 1-Wire BUS TO OTHER 1-Wire DEVICES Figure 1. Supplying the Parasite-Powered MAX31820PAR During Temperature Conversions www.maximintegrated.com Maxim Integrated 7 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor in Figure 1. The 1-Wire bus must be switched to the strong pullup within 10s (max) after a Convert T [44h] or Copy Scratchpad [48h] command is issued, and the bus must be held high by the pullup for the duration of the conversion (tCONV) or data transfer (tWR = 10ms). No other activity can take place on the 1-Wire bus while the pullup is enabled. 64-Bit Lasered ROM Code Each device contains a unique 64-bit code stored in ROM (Figure 2). The least significant 8 bits of the ROM code contain the device's 1-Wire family code, 28h. The next 48 bits contain a unique serial number. The most significant 8 bits contain 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 device to operate as a 1-Wire device using the protocol detailed in the 1-Wire Bus System section. Memory The device's memory is organized as shown in Figure 3. The memory consists of an SRAM scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (TH and TL) and configuration register. Note that if the device alarm function is not used, the TH and TL registers can serve as general-purpose memory. All memory commands are described in detail in the MAX31820PAR 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 TH and TL registers. Byte 4 contains the configuration register data, which is explained in detail in the Configuration Register section. Bytes 7:5 are reserved for internal use by the device and cannot be overwritten. Byte 8 of the scratchpad is read-only and contains the CRC code for bytes 7:0 of the scratchpad. The device generates this CRC using the method described in the CRC Generation section. MSb LSb 8-BIT CRC CODE MSb 8-BIT FAMILY CODE (28h) 48-BIT SERIAL NUMBER LSb MSb LSb MSb LSb Figure 2. 64-Bit Lasered ROM Code SCRATCHPAD (POWER-UP STATE SHOWN IN PARENTHESES) BYTE 0 TEMPERATURE REGISTER LSB (50h) BYTE 1 TEMPERATURE REGISTER MSB (05h) EEPROM BYTE 2 TH REGISTER OR USER BYTE 1* TH REGISTER OR USER BYTE 1 BYTE 3 TL REGISTER OR USER BYTE 2* TL 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. Figure 3. Memory Map www.maximintegrated.com Maxim Integrated 8 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Data is written to bytes 4:2 of the scratchpad using the Write Scratchpad [4Eh] command; the data must be transmitted to the device starting with the least significant bit of byte 2. To verify data integrity, the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least significant bit of byte 0. To transfer the TH, TL, 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 the device is powered down; at power-up the EEPROM data is reloaded into the corresponding scratchpad locations. Data can also be reloaded from EEPROM to the scratchpad at any time using the Recall E2 [B8h] command. The master can issue read time slots following the Recall E2 command, and the device indicates the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done. Configuration Register Byte 4 of the scratchpad memory contains the configuration register, which is organized as shown in Configuration Register Format. The user can set the conversion resolution of the device using the R0 and R1 bits in this register, as shown in Table 2. The power-up default of these bits is R0 = 1 and R1 = 1 (12-bit resolution). Note that there is a direct trade-off between resolution and conversion time. Bit 7 and bits 4:0 in the configuration register are reserved for internal use by the device and cannot be overwritten. Configuration Register Format BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 0 R1 R0 1 1 1 1 1 Table 2. Thermometer Resolution Configuration R1 R0 RESOLUTION (BITS) 0 0 9 93.75ms (tCONV/8) 0 1 10 187.5ms (tCONV/4) 1 0 11 375ms (tCONV/2) 1 1 12 750ms (tCONV) www.maximintegrated.com MAX CONVERSION TIME Maxim Integrated 9 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor POLYNOMIAL = X8 + X5 + X4 + 1 1ST STAGE X0 2ND STAGE X1 3RD STAGE X2 4TH STAGE X3 5TH STAGE X4 6TH STAGE X5 7TH STAGE X6 8TH STAGE X7 X8 INPUT DATA Figure 4. CRC Generator CRC Generation CRC bytes are provided as part of the device's 64-bit ROM code and in the 9th 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 therefore 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 device. To verify that data has been read correctly, the bus master must recalculate the CRC from the received data and then compare this value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for scratchpad reads). If the calculated CRC matches the read CRC, the data has been received error free. The comparison of CRC values and the decision to continue with an operation are determined entirely by the bus master. There is no circuitry inside the device that prevents a command sequence from proceeding if the device CRC (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 = X8 + X5 + X4 + 1 The bus master can recalculate the CRC and compare it to the CRC values from the MAX31820PAR using the polynomial generator shown in Figure 4. This circuit consists of a shift register and XOR gates, and the shift register bits are initialized to 0. Starting with the least significant bit of the ROM code or the least significant bit of byte 0 in the scratchpad, one bit at a time should be shifted into the shift register. After shifting in the 56th bit from the ROM or the most significant bit of byte 7 from the scratchpad, the polynomial generator contains the recalculated CRC. Next, the 8-bit ROM code or scratchpad CRC from the device must be shifted into the circuit. At this point, if the recalculated CRC was correct, the shift register contains all 0s. Additional information about the Maxim Integrated 1-Wire CRC is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton(R) Products. iButton is a registered trademark of Maxim Integrated Products, Inc. www.maximintegrated.com Maxim Integrated 10 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor VPU VPU STRONG PULLUP 1-Wire BUS RX DQ PIN RX 5A TYP TX MICROPROCESSOR MAX31820PAR 1-Wire PORT 4.7k RX = RECEIVE TX = TRANSMIT 100 MOSFET TX Figure 5. Hardware Configuration 1-Wire Bus System The 1-Wire bus system uses a single bus master to control one or more slave devices. The MAX31820PAR 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 multidrop 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, transaction sequence, and 1-Wire signaling (signal types and timing). Hardware Configuration The 1-Wire bus has, by definition, only a single data line. Each device (master or slave) interfaces to the data line through an open-drain or three-state port. This allows each device to release the data line when the device is not transmitting data so the bus is available for use by another device. The 1-Wire port of the MAX31820PAR (the DQ pin) is open drain with an internal circuit equivalent to that shown in Figure 5. The 1-Wire bus requires an external pullup resistor of approximately 5k; 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 480s, all components on the bus will be reset. Additionally, to ensure that the device www.maximintegrated.com 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. Transaction Sequence The transaction sequence for accessing the device is as follows: 1) Step 1: Initialization 2) Step 2: ROM command (followed by any required data exchange) 3) Step 3: MAX31820PAR Function command (followed by any required data exchange) It is very important to follow this sequence every time the device is accessed, as the device does not respond if any steps 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 master, followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that slave devices (such as the MAX31820PAR) are on the bus and are ready to operate. Timing for the reset and presence pulses is detailed in the 1-Wire Signaling section. Maxim Integrated 11 MAX31820PAR ROM Commands After the bus master has detected a presence pulse, it can issue a ROM command. These commands operate on the unique 64-bit ROM codes of each slave 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 present on the bus or if any device 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 MAX31820PAR Function command. Figure 6 shows a flowchart for operation of the ROM commands. Search ROM [F0h] When a system is initially powered up, the master must identify the ROM 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 cycle (i.e., Search ROM command followed by data exchange) as many times as necessary to identify all the slave devices. If there is only one slave on the bus, the simpler Read ROM command can be used in place of the Search ROM process. For a detailed explanation of the Search ROM procedure, refer to Application Note 937: Book of iButton Standards. 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 occurs when all the slaves attempt to respond at the same time. www.maximintegrated.com 1-Wire, Parasite-Power, Ambient Temperature Sensor 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 multidrop or single-drop bus. Only the slave that exactly matches the 64-bit ROM code sequence responds to the function command issued by the master; all other slaves on the bus wait for a reset pulse. Skip ROM [CCh] The master can use this command to address all devices on the bus simultaneously, without sending out any ROM code information. For example, the master can make all devices on the bus perform simultaneous temperature conversions by issuing a Skip ROM command followed by a Convert T [44h] command. Note that the Read Scratchpad [BEh] command can follow the Skip ROM command only if there is a single slave device on the bus. In this case, time is saved by allowing the master to read from the slave without sending the device's 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad command causes a data collision on the bus if there is more than one slave since multiple devices 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 respond. This command allows the master device to determine if any MAX31820PARs 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 (initialization) in the transaction sequence. See the Alarm Signaling section for an explanation of alarm flag operation. Maxim Integrated 12 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor INITIALIZATION SEQUENCE MASTER TX RESET PULSE DEVICE TX PRESENCE PULSE MASTER TX ROM COMMAND 33h READ ROM? N Y 55h MATCH ROM? F0h SEARCH ROM? N Y Y DEVICE TX BIT 0 MASTER TX BIT 0 BIT 0 MATCH? N N DEVICE TX SERIAL NUMBER 6 BYTES DEVICE TX CRC BYTE N Y CCh SKIP ROM? N Y DEVICE TX BIT DEVICE TX BIT 0 DEVICE TX BIT MASTER TX BIT 0 BIT 0 MATCH? DEVICE(S) WITH ALARM FLAG SET? Y N Y DEVICE TX BIT 1 MASTER TX BIT 1 BIT 1 MATCH? ECh ALARM SEARCH COMMAND MASTER TX BIT 0 Y DEVICE TX FAMILY CODE 1 BYTE N DEVICE TX BIT 1 MASTER TX BIT 1 N N BIT 1 MATCH? Y Y DEVICE TX BIT 63 MASTER TX BIT 63 BIT 63 MATCH? DEVICE TX BIT 63 MASTER TX BIT 63 N N BIT 63 MATCH? Y Y MASTER TX FUNCTION COMMAND Figure 6. ROM Commands Flowchart www.maximintegrated.com Maxim Integrated 13 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor MAX31820PAR Function Commands After the bus master has used a ROM command to address the device with which it wishes to communicate, the master can issue one of the device function commands. These commands allow the master to write to and read from the device's scratchpad memory, initiate temperature conversions, and determine the power-supply mode. Table 3 summarizes the device function commands, and Figure 7 illustrates the function commands. Convert T [44h] This command initiates a single temperature conversion. Following the conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratchpad memory and the device returns to its low-power idle state. Within 10s (max) after this command is issued, the master must enable a strong pullup on the 1-Wire bus for the duration of the conversion (tCONV), as described in the Parasite Power section. Write Scratchpad [4Eh] This command allows the master to write 3 bytes of data to the device's scratchpad. The first data byte is written into the TH register (byte 2 of the scratchpad), the second byte is written into the TL register (byte 3), and the third byte is written into the configuration register (byte 4). Data must be transmitted least significant bit first. All three bytes must be written before 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 continues through the scratchpad until the 9th byte (byte 8 - CRC) is read. The master can issue a reset to terminate reading at any time if only part of the scratchpad data is needed. Copy Scratchpad [48h] This command copies the contents of the scratchpad TH, TL and configuration registers (bytes 2, 3, and 4) to EEPROM. Within 10s (max) after this command is issued, the master must enable a strong pullup on the 1-Wire bus for at least 10ms as described in the Parasite Power section. Recall E2 [B8h] This command recalls the alarm trigger values (TH and TL) and configuration data 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 following the Recall E2 command and the device indicates the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done. The recall operation happens automatically at power-up, so valid data is available in the scratchpad as soon as power is applied to the device. Table 3. MAX31820PAR Function Command Set COMMAND Convert T (Note 1) DESCRIPTION PROTOCOL 1-Wire BUS ACTIVITY AFTER COMMAND IS ISSUED Initiates temperature conversion. 44h None. Read Scratchpad (Note 2) Reads the entire scratchpad including the CRC byte. BEh The device transmits up to 9 data bytes to master. Write Scratchpad (Note 3) Writes to scratchpad bytes 2, 3, and 4 (TH, TL, and configuration registers). 4Eh The master transmits 3 data bytes to the device. Copy Scratchpad (Note 1) Copies TH, TL, and configuration register data from the scratchpad to EEPROM. 48h None. Recall E2 Recalls TH, TL, and configuration register data from EEPROM to the scratchpad. B8h The device transmits recall status to the master. Note 1: The master must enable a strong pullup on the 1-Wire bus during temperature conversions and copies from the scratchpad to EEPROM. No other bus activity can take place during this time. Note 2: The master can interrupt the transmission of data at any time by issuing a reset. Note 3: All 3 bytes must be written before a reset is issued. www.maximintegrated.com Maxim Integrated 14 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor 44h CONVERT T? MASTER TX FUNCTION COMMAND 48h COPY SCRATCHPAD? N Y N N Y MASTER ENABLES STRONG PULLUP ON DQ MASTER ENABLES STRONG PULLUP ON DQ DEVICE CONVERTS TEMPERATURE DATA COPIED FROM SCRATCHPAD TO EEPROM MASTER DISABLES STRONG PULLUP MASTER DISABLES STRONG PULLUP B8h RECALL E2 ? N BEh READ SCRATCHPAD ? N Y Y 4Eh WRITE SCRATCHPAD ? Y MASTER TX TH BYTE TO SCRATCHPAD MASTER BEGINS DATA RECALL FROM E2 PROM MASTER TX RESET? DEVICE BUSY RECALLING DATA ? Y MASTER RX "0s" MASTER TX TL BYTE TO SCRATCHPAD MASTER RX DATA BYTE FROM SCRATCHPAD N N N MASTER RX "1s" Y MASTER TX CONFIG. BYTE TO SCRATCHPAD HAVE 8 BYTES BEEN READ? Y MASTER RX SCRATCHPAD CRC BYTE RETURN TO INITIALIZATION SEQUENCE FOR NEXT TRANSACTION Figure 7. MAX31820PAR Function Commands Flowchart www.maximintegrated.com Maxim Integrated 15 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor 1-Wire Signaling as illustrated in Figure 8. When the device 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. The MAX31820PAR uses a strict 1-Wire communication protocol to ensure data integrity. Several signal types are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. The bus master initiates all these signals, with the exception of the presence pulse. Initialization Procedure: Reset and Presence Pulses All communication with the device begins with an initialization sequence that consists of a reset pulse from the master followed by a presence pulse from the device, During the initialization sequence, the bus master transmits (TX) the reset pulse by pulling the 1-Wire bus low for a minimum of 480s. The bus master then releases the bus and goes into receive mode (RX). When the bus is released, the 5k pullup resistor pulls the 1-Wire bus high. When the device detects this rising edge, it waits 15s to 60s and then transmits a presence pulse by pulling the 1-Wire bus low for 60s to 240s. MASTER TX RESET PULSE 480s MINIMUM VPU DEVICE WAITS 15s TO 60s MASTER RX 480s MINIMUM DEVICE TX PRESENCE PULSE 60s TO 240s 1-Wire BUS GND BUS MASTER PULLING LOW DEVICE PULLING LOW RESISTOR PULLUP Figure 8. Initialization Timing www.maximintegrated.com Maxim Integrated 16 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Read/Write Time Slots slots. Both types of write time slots are initiated by the master pulling the 1-Wire bus low (Figure 9). The bus master writes data to the device during write time slots and reads data from the device during read time slots. One bit of data is transmitted over the 1-Wire bus per time slot. To generate a write-one time slot, after pulling the 1-Wire bus low, the bus master must release the 1-Wire bus within 15s. When the bus is released, the 5k pullup resistor pulls the bus high. To generate a write-zero time slot, after pulling the 1-Wire bus low, the bus master must continue to hold the bus low for the duration of the time slot (at least 60s). Write Time Slots There are two types of write time slots: write-one time slots and write-zero time slots. The bus master uses a write-one time slot to write a logic 1 to the device and a write-zero time slot to write a logic 0 to the device. All write time slots must be a minimum of 60s in duration with a minimum of a 1s recovery time between individual write The device samples the 1-Wire bus during a window that lasts from 15s to 60s after the master initiates the write time slot. If the bus is high during the sampling window, a 1 is written to the device. If the line is low, a 0 is written to the device. START OF SLOT START OF SLOT MASTER WRITE-ZERO SLOT 1s < tREC < 60s < TX "0" < 120s MASTER WRITE-ONE SLOT > 1s VPU 1-Wire BUS GND DEVICE SAMPLES MIN 15s TYP 15s DEVICE SAMPLES MAX MIN 30s 15s MASTER READ-ZERO SLOT TYP MAX 15s 30s MASTER READ-ONE SLOT 1s < tREC < VPU 1-Wire BUS GND MASTER SAMPLES > 1s MASTER SAMPLES > 1s 15s 45s BUS MASTER PULLING LOW 15s DEVICE PULLING LOW RESISTOR PULLUP Figure 9. Read/Write Time Slot Timing Diagram www.maximintegrated.com Maxim Integrated 17 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Read Time Slots The device can only transmit data to the master when the master issues read time slots. Therefore, the master must generate read time slots immediately after issuing a Read Scratchpad [BEh] command, so that the device can provide the requested data. In addition, the master can generate read time slots after issuing a Recall E2 [B8h] command to find out the status of the operation, as explained in the Parasite Power section. All read time slots must be a minimum of 60s in duration with a minimum of a 1s recovery time between slots. A read time slot is initiated by the master device pulling the 1-Wire bus low for a minimum of 1s and then releasing the bus (Figure 9). After the master initiates the read time slot, the device begins transmitting a 1 or 0 on the bus. The device transmits a 1 by leaving the bus high and transmits a 0 by pulling the bus low. When transmitting a 0, the device releases the bus by the end of the time slot, and the bus is pulled back to its high idle state by the pullup resister. Output data from the device is valid for 15s after the falling edge that initiated the read time slot. Therefore, the master must release the bus and then sample the bus state within 15s from the start of the slot. Figure 10 illustrates that the sum of tINIT, tRC, and tSAMPLE must be less than 15s for a read time slot. Figure 11 shows that system timing margin is maximized by keeping tINIT and tRC as short as possible and by locating the master sample time during read time slots towards the end of the 15s period. VPU VIH OF MASTER 1-Wire BUS GND tINIT > 1s tRC MASTER SAMPLES 15s BUS MASTER PULLING LOW RESISTOR PULLUP Figure 10. Detailed Master Read-One Timing VPU VIH OF MASTER 1-Wire BUS GND tINIT = SMALL MASTER SAMPLES tRC = SMALL 15s BUS MASTER PULLING LOW RESISTOR PULLUP Figure 11. Recommended Master Read-One Timing www.maximintegrated.com Maxim Integrated 18 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Operation Examples Example 2 Example 1 In Table 4 there are multiple devices on the bus. The bus master initiates a temperature conversion in a specific MAX31820PAR and then reads its scratchpad and recalculates the CRC to verify the data. In Table 5 there is only one device on the bus. The master writes to the TH, TL, and configuration registers in the device's scratchpad and then reads the scratchpad and recalculates the CRC to verify the data. The master then copies the scratchpad contents to EEPROM. Table 4. Operation Example 1 MASTER MODE DATA (LSB FIRST) COMMENTS Tx Reset Rx Presence Devices respond with presence pulse. Master issues reset pulse. Tx 55h Master issues Match ROM command. Tx 64-bit ROM code Tx 44h Tx DQ line held high by strong pullup Tx Reset Rx Presence Devices respond with presence pulse. Tx 55h Master issues Match ROM command. Tx 64-bit ROM code Tx BEh Rx 9 data bytes Master sends device ROM code. Master issues Convert T command. Master applies strong pullup to DQ for the duration of the conversion (tCONV). Master issues reset pulse. Master sends device ROM code. Master issues Read Scratchpad command. Master reads entire scratchpad including CRC. The master then recalculates the CRC of the first 8 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. Table 5. Operation Example 2 MASTER MODE DATA (LSB FIRST) COMMENTS Tx Reset Rx Presence Master issues reset pulse. Tx CCh Master issues Skip ROM command. Tx 4Eh Master issues Write Scratchpad command. Tx 3 data bytes Tx Reset Rx Presence Tx CCh Master issues Skip ROM command. Tx BEh Master issues Read Scratchpad command. Rx 9 data bytes Device responds with presence pulse. Master sends 3 data bytes to the scratchpad (TH, TL, and configuration registers). Master issues reset pulse. Device responds with presence pulse. Master reads entire scratchpad including CRC. The master then recalculates the CRC of the first 8 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 Rx Presence Tx CCh Master issues Skip ROM command. Tx 48h Master issues Copy Scratchpad command. Tx DQ line held high by strong pullup www.maximintegrated.com Master issues reset pulse. Device responds with presence pulse. Master applies strong pullup to DQ for at least 10ms while copy operation is in progress. Maxim Integrated 19 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Ordering Information PART TEMP RANGE PIN-PACKAGE MAX31820PARMCR+ -55C to +125C 3 TO-92 (straight leads) MAX31820PARMCR+T -55C to +125C 3 TO-92 (formed leads) +Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 3 TO-92 (straight leads) Q3+1 21-0248 -- 3 TO-92 (formed leads) Q3+4 21-0250 -- www.maximintegrated.com Maxim Integrated 20 MAX31820PAR 1-Wire, Parasite-Power, Ambient Temperature Sensor Revision History REVISION NUMBER REVISION DATE 0 6/13 DESCRIPTION Initial release PAGES CHANGED -- For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated's website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. (c) 2013 Maxim Integrated Products, Inc. 21 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX31820PARMCR+T MAX31820PARMCR+