MAXIM DS1825 Manual
Contents
1. MASTER Tx RESET MASTER Tx CONFIG BYTE DEVICE BUSY RECALLING N TO SCRATCHPAD DATA HAVE 8 BYTES BEEN READ MASTER MASTER Y Rx Os Rx 4s MASTER Ry SCRATCHPAD CRC BYTE RETURN TO INITIALIZATION SEQUENCE FIGURE 11 FOR NEXT TRANSACTION 14 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID SUGGESTED PROCEDURE FOR BUILDING CROSS REFERENCE TABLE This procedure uses the Search ROM command to find all DS1825s on the one wire bus 16 maximum and then reads each configuration register to match the ROMIDs to the hard wired addresses Figure 13 Search all ROMIDs on bus amp BUILDING store ROMIDs CROSSREFERENCE FOh command TABLE USING ROMIDS AND 4 BIT Y ADDRESSES Y Increment Counter N Nmax 2 N N 1 Nmax is the number of ROMIDs found Master Tx Next ROMID Crossreference Table ROMID AD3 ADO Recall EEPROM ROMID 0 0000 trom Contig Dd rid Register ROMID 2 0010 ROMID 3 0011 O O O O Match ROMID to O O Address and Add ROMID 12 1100 to Crossreference Table ROMID 13 1101 ROMID 14 1110 ROMID 15 1111 Note Temperature sensors are addressed by ROMID not by binary address 15 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID 1 Wire SIGNALING Th2. 33h READ ROM COMMAND 55h MATCH ROM COMMAND MASTER Tx BIT 0 FOh SEARCH ROM COMMAND CCh SKIP ROM COMMAND COMMAND DS1825 Tx BIT 0 DS1825 Tx BIT 0 MASTER Tx BIT 0 DS1825 Tx FAMILY CODE 1 BYTE N aro aro exce 2 MATOH MATCH FLAG SET DS1825 Tx SERIAL NUMBER 6 BYTES DS1825 Tx BIT 1 DS1825 Tx MASTER Tx CRC BYTE BIT 1 DS1529 DOBIESE MASTER T BIT 1 Y DS1825 Tx BIT 63 MASTER Tx DS1825 Tx BIT 63 BIT 63 MASTER Tx BIT 63 N BIT 63 BIT 63 MATCH MATCH MASTER Tx FUNCTION COMMAND FIGURE 12 13 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 12 D81825 FUNCTION COMMANDS FLOW CHART 44h CONVERT TEMPERATURE 2 48h COPY SCRATCHPAD MASTER Tx FUNCTION COMMAND PARASITE POWER PARASITE POWER DS1825 BEGINS MASTER ENABLES CONVERSION STRONG PULL UP ON DQ DATA COPIED FROM SCRATCHPAD TO EEPROM MASTER DISABLES STRONG PULLUP DEVICE CONVERTING TEMPERATURE COPY IN PROGRESS MASTER Rx Os MASTER Rx 1s BEh 4Eh N E E N READ N WRITE 1 SCRATCHPAD SCRATCHPAD r E Y Y Y MASTER Tx Ty BYTE PARASITE POWERED 2 MASTER MASTER Rx 1s Rx Os MASTER BEGINS DATA RECALL FROM E PROM MASTER Rx DATA BYTE TO SCRATCHPAD FROM SCRATCHPAD MASTER Tx T BYTE TO SCRATCHPAD
3. 1 us Trec lt 0 DS1825 Samples DS1825 Samples MIN TYP MAX MIN TYP MAX 15s gt lt 15 us 30 us lt 15ys lt 15 us 30 us MASTER READ 0 SLOT MASTER READ 1 SLOT 1 us Trec oo gt gt Master samples e I Master samples lc 15js sea 45 us 15 us LINE TYPE LEGEND Bus master pulling low DS1825 pulling low Resistor pullup READ TIME SLOTS The DS1825 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 or Read Power Supply B4h command so that the DS1825 can provide the requested data In addition the master can generate read time slots after issuing Convert T 44h or Recall E B8h commands to find out the status of the operation as explained in the D81825 FUNCTION COMMAND section All read time slots must be a minimum of 60us in duration with a minimum of a 1us recovery time between slots A read time slot is initiated by the master device pulling the 1 Wire bus low for a minimum of 1us and then releasing the bus see Figure 14 After the master initiates the read time slot the DS1825 will begin transmitting a 1 or O on bus The DS1825 transmits a 1 by leaving the bus high and transmits a 0 by pulling the bus low When transmitting a 0 the DS1825 will release the bus by the end of the time slot and the bus
4. iPDHIGH 19 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 20 ADDRESS PROGRAMMING DIAGRAM Vpp POWERED 1 Wire Bus Location O ADO GND AD1 GND AD2 GND AD3 GND Location 1 ADO VDD AD1 GND AD2 GND AD3 GND Location 2 ADO GND AD1 AD1 VDD VDD AD2 AD2 GND GND AD3 AD3 GND Location 15 ADO VDD AD1 VDD AD2 VDD AD3 VDD Note ADO AD3 cannot float each pin must be tied to either Vpp or GND 20 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 21 ADDRESS PROGRAMMING DIAGRAM PARASITE POWERED 1 Wire Bus Location O ADO GND AD1 GND AD2 GND AD3 GND Location 1 ADO VDD AD1 GND VDD AD2 GND GND AD3 AD3 GND LL Location 2 ADO ADO GND AD1 AD1 VDD VDD AD2 AD2 GND GND AD3 AD3 GND S Location 15 ADO ADO VDD AD1 AD1 VDD VDD AD2 AD2 VDD GND AD3 AD3 VDD Note ADO AD3 cannot float each pin must be tied to either Voo or GND 21 of 21
5. Digital Thermometer With 4 Bit ID Figure 3 Ty AND T REGISTER FORMAT bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit O S 29 25 2 25 2 21 29 Only bits 11 through 4 of the temperature register are used in the Ty and T comparison since Ty and T are 8 bit registers If the measured temperature is lower than or equal to T or higher than or equal to Ty an alarm condition exists and an alarm flag is set inside the DS1825 This flag is updated after every temperature measurement therefore if the alarm condition goes away the flag will be turned off after the next temperature conversion The master device can check the alarm flag status of all DS1825s on the bus by issuing an Alarm Search ECh command Any DS1825s with a set alarm flag will respond to the command so the master can determine exactly which DS1825s have experienced an alarm condition If an alarm condition exists and the Ty or T settings have changed another temperature conversion should be done to validate the alarm condition POWERING THE DS1825 The DS1825 can be powered by an external supply on the Vpp pin or it can operate in parasite power mode which allows the DS1825 to function without a local external supply Parasite power is very useful for applications that require remote temperature sensing or that are very space constrained Figure 1 shows the DS1825 s parasite power control circuitry which steals power from the 1 Wire
6. Issu d Notes TEMPERATURE CONVERSION COMMANDS initiates temperat re DS1825 transmits conversion status Convert T eSnversi ri p 44h to master not applicable for 1 parasite powered DS1825s MEMORY COMMANDS Reads the entire scratchpad DS1825 transmits up to 9 data Read peraichped including the CRC byte BEN bytes to master 2 Writes data into scratchpad Write Scratchpad bytes 2 3 and 4 Ty Tu and dpi ddasteruonstulie 3 data vtae te 3 DS1825 configuration registers Copies Ty TL and configuration register data Copy Scratchpad from the scratchpad to 48h None 1 EEPROM Recalls Ty T and 2 configuration register data DS1825 transmits recall status to mecal E from EEPROM to the Bon master scratchpad Read Power Signals DS1825 power supply B4h DS1825 transmits supply status to Supply mode to the master master NOTES 1 For parasite powered DS1825s 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 may take place during this time The master can interrupt the transmission of data at any time by issuing a reset All three bytes must be written before a reset is issued wN 12 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 11 ROM COMMANDS FLOW CHART Initialization MASTER Tx Sequence RESET PULSE DS1825 Tx PRESENCE PULSE MASTER Tx ROM COMMAND
7. Os Additional information about the Dallas 1 Wire cyclic redundancy check is available in Application Note 27 entitled Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor Touch Memory Products Figure 9 CRC GENERATOR 1 Wire BUS SYSTEM The 1 Wire bus system uses a single bus master to control one or more slave devices The DS1825 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 9 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID 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 3 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 DS1825 the DQ pin is open drain with an internal circuit equivalent to that shown in Figure 10 The 1 Wire bus requires an external pullup resistor of approximately 5kQ thus the idle state for the 1 Wire bus is high If
8. 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 480us all components on the bus will be reset Figure 10 HARDWARE CONFIGURATION DS1825 1 WIRE PORT 4 7K 1 Wire Bus MOSFET Rx RECEIVE Tx gt TRANSMIT TRANSACTION SEQUENCE The transaction sequence for accessing the DS1825 is as follows Step 1 Initialization Step 2 ROM Command followed by any required data exchange Step 3 DS1825 Function Command followed by any required data exchange It is very important to follow this sequence every time the DS1825 is accessed as the DS1825 will not respond if any steps in the sequence are missing or out of order Exceptions to this rule are the Search ROM FOh 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 DS1825 are on the bus and are ready to operate Timing for the reset and presence pulses is detailed in
9. numbers S 0 and for negative numbers S 1 If the DS1825 is configured for 12 bit resolution all bits in the temperature register will contain valid data For 11 bit resolution bit O is undefined For 10 bit resolution bits 1 and O are undefined and for 9 bit resolution bits 2 1 and O are undefined Table 3 gives examples of digital output data and the corresponding temperature reading for 12 bit resolution conversions Figure 2 TEMPERATURE REGISTER FORMAT bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit O LS Byte 2 2 2 2 2 2 27 a bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8 MS Byte S S S S S 2 25 2 Table 3 TEMPERATURE DATA RELATIONSHIP TEMPERATURE DIGITAL OUTPUT DIGITAL OUTPUT Binary Hex The power on reset value of the temperature register is 85 C OPERATION ALARM SIGNALING After the DS1825 performs a temperature conversion the temperature value is compared to the user defined two s complement alarm trigger values stored in the 1 byte Ty and T registers see Figure 3 The sign bit S indicates if the value is positive or negative for positive numbers S 0 and for negative numbers S 1 The Ty and T registers are NV EEPROM so they will retain data when the device is powered down T4 and T can be accessed through bytes 2 and 3 of the scratchpad as explained in the MEMORY section of this data sheet 5 of 21 DS1825 Programmable Resolution 1 Wire
10. the DS1825 To verify that data has been read correctly the bus master must re calculate 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 DS1825 that prevents a command sequence from proceeding if the DS1825 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 2X x X 14 The bus master can re calculate the CRC and compare it to the CRC values from the DS1825 using the polynomial generator shown in Figure 9 This circuit consists of a shift register and XOR gates and the shift register bits are initialized to O 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 shifted into the shift register After shifting in the 56 bit from the ROM or the most significant bit of byte 7 from the scratchpad the polynomial generator will contain the re calculated CRC Next the 8 bit ROM code or scratchpad CRC from the DS1825 must be shifted into the circuit At this point if the re calculated CRC was correct the shift register will contain all
11. to Vpp or GND Pins tied to DQ Vpp are reported with a logical 1 and pins tied to GND are reported as a logical 0 Pins connected to DQ Vpp or GND through a resistor are valid logical 1s or logical Os if the resistor is less than 10k Floating or high impedance gt 10kQ connections are indeterminate Bit 7 and Bit 4 of the configuration register are reserved for internal use and cannot be overwritten Figure 8 CONFIGURATION REGISTER FORMAT Note Bit 0 through Bit 3 are programmed through the four Location Programming Address pins ADO AD3 Reading the configuration register provides location information on up to 16 individual DS1825s bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 co Th e i e 8 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Table 4 THERMOMETER RESOLUTION CONFIGURATION Rt RO Resolution _ Max Conversion Time 0o o 9 9375ms tconv 8 I 8 21 4 10 bit 187 5ms tconv 4 a o ni cow iz TNT CRC GENERATION CRC bytes are provided as part of the DS1825 s 64 bit ROM code and in the g 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 it changes when the data in the scratchpad changes The CRCs provide the bus master with a method of data validation when data is read from
12. will be pulled back to its high idle state by the pullup resister Output data from the DS1825 is valid for 15us after the falling edge that initiated the read time slot Therefore the master must release the bus and then sample the bus state within 15us from the start of the slot Figure 15 illustrates that the sum of Tyr Tac and Tsayp g must be less than 15us for a read time slot Figure 16 shows that system timing margin is maximized by keeping Tir and Trc as short as possible and by locating the master sample time during read time slots towards the end of the 15us period 17 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 16 DETAILED MASTER READ 1 TIMING VIH of Master lt Twr gt 1ps gt Tr _ Mastersamples 4 15us Figure 17 RECOMMENDED MASTER READ 1 TIMING VIH of Master lt gt Tint Tre small small Master samples 1 15us LINE TYPE LEGEND mu Bus master pulling low DS1825 OPERATION EXAMPLE In this example there are multiple DS1825s on the bus and they are using parasite power The bus master initiates a temperature conversion in a specific DS1825 and then reads its scratchpad and recalculates the CRC to verify Resistor pullup the data MASTER MODE DATA LSB FIRST COMMENTS TX Reset Master issues reset pulse RX Pre
13. aaa aaa eee DS1825 m Programmable Resolution 1 Wire m DALLAS y e DALLAS AVLA KIA Digital Thermometer With 4 Bit ID Lwww maxim ic com a EEEEULAARA FEATURES PIN ASSIGNMENT Unique 1 Wire Interface Requires Only One Port Pin for Communication Each Device has a Unique 64 Bit Serial Code Stored in an On Board ROM Multidrop Capability Simplifies Distributed Temperature Sensing Applications 4 Pin Programmable Bits to Uniquely Identify Up to 16 Sensor Locations on a Bus Requires No External Components Can be Powered from Data Line Power Supply Range 3 0V to 3 7V Measures Temperatures from 55 C to 125 C 67 F to 257 F 0 5 C Accuracy from 10 C to 85 C Thermometer Resolution is User Selectable from 9 to 12 Bits DS1825U Converts Temperature to 12 Bit Digital Word in 750ms max User Definable NV Alarm Settings PIN DESCRIPTION Alarm Search Command Identifies and GND Ground Addresses Devices Whose Temperature is DQ Data In Out Outside of Programmed Limits Temperature N C No Connect Alarm Condition Vbp Power Supply Voltage Available in 8 Pin SOP Package ADO to AD3 Address Pins Software Compatible with the DS1822 APPLICATIONS Thermostatic Controls Industrial Systems Consumer Products Thermometers Thermally Sensitive Systems 1 Wire is a registered trademark of Dallas Semiconductor DESCRIPTION The DS1825 digital thermometer provides 9 to 12 bit centigrad
14. bus through the DQ pin when the bus is high The stolen charge powers the DS1825 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 When the DS1825 is used in parasite power mode the Vpp pin must be connected to ground In parasite power mode the 1 Wire bus and Cpp can provide sufficient current to the DS1825 for most operations as long as the specified timing and voltage requirements are met refer to the DC ELECTRICAL CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this data sheet However when the DS1825 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 assure that the DS1825 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 in Figure 4 The 1 Wire bus must be switched to the strong pullup within 10us 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 tsonv or data transfer ty 10ms No othe
15. e DS1825 uses a strict 1 Wire communication protocol to insure data integrity Several signal types are defined by this protocol reset pulse presence pulse write 0 write 1 read 0 and read 1 All of these signals with the exception of the presence pulse are initiated by the bus master INITIALIZATION PROCEDURE RESET AND PRESENCE PULSES All communication with the DS1825 begins with an initialization sequence that consists of a reset pulse from the master followed by a presence pulse from the DS1825 This is illustrated in Figure 13 When the DS1825 sends the presence pulse in response to the reset it is indicating to the master that it is on the bus and ready to operate During the initialization sequence the bus master transmits Tx the reset pulse by pulling the 1 Wire bus low for a minimum of 480us 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 DS1825 detects this rising edge it waits 15 60ys and then transmits a presence pulse by pulling the 1 Wire bus low for 60 240us Figure 14 INITIALIZATION TIMING MASTER Tx RESET PULSE MASTER Rx 480 us minimum lt WW______ 480 ps minimum DS1825 Tx DS1825 presence pulse waits 15 60 us 60 240 us LINE TYPE LEGEND mm Bus master pulling low DS1825 pulling low Resistor pullup READ WRITE TIME SLOTS The bus master writes data to t
16. e temperature measurements and has an alarm function with NV user programmable upper and lower trigger points The DS1825 communicates over a 1 Wire bus that by definition requires only one data line and ground for communication with a central microprocessor It has an operating temperature range of 55 C to 125 C and is accurate to 0 5 C over the range of 10 C to 85 C In addition the DS1825 can derive power directly from the data line parasite power eliminating the need for an external power supply ORDERING INFORMATION ORDERING NUMBER PACKAGE MARKING DESCRIPTION DS1825U 1825 8 pin SOP DS1825U T amp R 1825 8 pin uSOP Tape and Reel DS1825U 1825 See Note 1 8 pin uSOP Lead Free DS1825U T amp R 1825 See Note 1 8 pin uSOP Tape and Reel Lead Free Note 1 Additionally a symbol will be marked on the package 1 of 21 Rev 020105 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID DESCRIPTION cont Each DS1825 has a unique 64 bit serial code which allows multiple DS1825s to function on the same 1 Wire bus thus it is simple to use one microprocessor to control many DS1825s distributed over a large area In addition the 4 bit location address can be used to identify specific temperature sensors in the system without requiring a wide lookup table Applications that can benefit from this feature include HVAC environmental controls temperature monitoring systems in
17. he DS1825 during write time slots and reads data from the DS1825 during read time slots One bit of data is transmitted over the 1 Wire bus per time slot WRITE TIME SLOTS There are two types of write time slots Write 1 time slots and Write 0 time slots The bus master uses a Write 1 time slot to write a logic 1 to the DS1825 and a Write 0 time slot to write a logic 0 to the DS1825 All write time slots must be a minimum of 60us in duration with a minimum of a lus recovery time between individual write slots Both types of write time slots are initiated by the master pulling the 1 Wire bus low see Figure 14 To generate a Write 1 time slot after pulling the 1 Wire bus low the bus master must release the 1 Wire bus within 15us When the bus is released the 5k pullup resistor will pull the bus high To generate a Write O 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 60us The DS1825 samples the 1 Wire bus during a window that lasts from 15us to 60us after the master initiates the write time slot If the bus is high during the sampling window a 1 is written to the DS1825 If the line is low a 0 is written to the DS1825 16 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 15 READ WRITE TIME SLOT TIMING DIAGRAM START START OF SLOT OF SLOT MASTER WRITE 0 SLOT MASTER WRITE 1 SLOT
18. in port the DQ pin in the case of the DS1825 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 of this data sheet Another feature of the DS1825 is the ability to 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 As an alternative the DS1825 can also be powered by an external supply on Vpp Figure 1 DS1825 BLOCK DIAGRAM VPULLUP Memory Control Logic Parasite Power Circuit 16 bit Temp Reg 64 Bit ROM And 1 wire Port 8 bit TH Register 8 bit TL Register 8 bit CRC Gen Orvar DOM 8 bit Config Reg Address Pin Input Latch ADO AD3 4 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID OPERATION MEASURING TEMPERATURE The core functionality of the DS1825 is its direct to digital temperature sensor The resol
19. in the LSB and the MSB of the temperature register respectively These bytes are read only Bytes 2 and 3 provide access to T4 and T registers Byte 4 contains the configuration register data which is explained in detail in the CONFIGURATION REGISTER section of this data sheet Bytes 5 6 and 7 are reserved for internal use by the device and cannot be overwritten 7 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Byte 8 of the scratchpad is read only and contains the cyclic redundancy check CRC code for bytes 0 through 7 of the scratchpad The DS1825 generates this CRC using the method described in the CRC GENERATION section Data is written to bytes 2 3 and 4 of the scratchpad using the Write Scratchpad 4Eh command the data must be transmitted to the DS1825 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 Ty T 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 including the hard wired address inputs ADO AD3 is reloaded into the corresponding scratchpad locations Data can also be reloaded f
20. istors are used their maximum values are 10 0000 2 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID AC ELECTRICAL CHARACTERISTICS NV MEMORY 55 C to 100 C Vpp 3 0V to 3 7V PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NV Write Cycle Time twr 2 10 ms EEPROM Writes Neewr 55 C to 55 C 50k writes EEPROM Data Retention tEEDR 55 C to 55 C 10 years AC ELECTRICAL CHARACTERISTICS 55 C to vies E NE SOV UE HA D PARAMETER SYMBOL CONDITION MIN UNITS NOTES 9 bit resolution 3375 ms 1 Temperature Conversion t 10 bit resolution 187 5 ms 1 Time ESNY 11 bit resolution 375 ms 1 12 bit resolution 750 ms 1 Start Convert T 10 HS Time to Strong Pullup On tspon Conimapndssued Time Slot tsi oT 60 120 us 1 Recovery Time trec 1 us 1 Write 0 Low Time tiowo 60 120 us 1 Write 1 Low Time tiow1 1 15 us 1 Read Data Valid trov 15 us 1 Reset Time High RSTH 480 us 1 Reset Time Low tRsTL 480 us 1 2 Presence Detect High tepuicH 15 60 us 1 Presence Detect Low tepLow 60 240 us 1 Capacitance DQ CiN oUT 25 pF Capacitance ADO AD3 Cin ap 50 pF NOTES 1 Refer to timing diagrams in Figure 18 2 Under parasite power if trst gt 960us a power on reset may occur Table 1 DETAILED PIN DESCRIPTIONS PIN SYMBOL DESCRIPTION 4 GND Ground 2 Data Input Output pin Ope
21. n drain 1 Wire interface pin Also DQ provides power to the device when used in parasite power mode see Parasite Power section 1 V Optional Vpp pin Voo must be grounded for operation in parasite 2D power mode 5 ADO Location Address Input Pin LSB 6 AD1 Location Address Input Pin 7 AD2 Location Address Input Pin 8 AD3 Location Address Input Pin MSB 3 N C No Connection 3 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID OVERVIEW Figure 1 shows a block diagram of the DS1825 and pin descriptions are given in Table 1 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 registers Ty and T 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 It is also used for the hard wired address programmed by the ADO AD3 pins The Ty TL and configuration registers are NV EEPROM so they will retain data when the device is powered down The DS1825 uses Dallas exclusive 1 Wire bus protocol that implements bus communication using one control signal The control line requires a weak pullup resistor since all devices are linked to the bus through a 3 state or open dra
22. p device is ideal and therefore the high level of the pullup is equal to Vpu In order to meet the Vin spec of the DS1825 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 Veu_actuat Vpu ipEAL VrRANSISTOR 3 See typical performance curve in Figure 18 4 Logic low voltages are specified at a sink current of 4mA 5 To guarantee a presence pulse under low voltage parasite power conditions Vi ux may have to be reduced to as low as 0 5V 6 Logic high voltages are specified at a source current of 1mA 7 Standby current specified up to 70 C Standby current typically is 3uA at 125 C 8 To minimize Ibos DQ should be within the following ranges GND lt DQ lt GND 0 3V or Vpp 0 3V x DQ lt Vpp 9 Active current refers to supply current during active temperature conversions or EEPROM writes 10 DQ line is high hi Z state 11 Drift data is based on a 1000 hour stress test at 125 C 12 Inputs ADO AD3 must be tied either High or Low A Low is a connection to the GND terminal A High connection varies with usage of the DS1825 When connected as a parasite powered sensor a connection to DQ is considered a High When powered through the Vpp pin a connection to Vpp is a High If left floating the input values are indeterminate and may be either logical 0 or logical 1 See Figures 20 and 21 for details When optional programming res
23. r activity can take place on the 1 Wire bus while the pullup is enabled The DS1825 can also be powered by the conventional method of connecting an external power supply to the Vpp pin as shown in Figure 5 The advantage of this method is that the MOSFET pullup is not required and the 1 Wire bus is free to carry other traffic during the temperature conversion time The use of parasite power is not recommended for temperatures above 100 C since the DS1825 may not be able to sustain communications due to the higher leakage currents that can exist at these temperatures For applications in which such temperatures are likely it is strongly recommended that the DS1825 be powered by an external power supply In some situations the bus master may not know whether the DS1825s on the bus are parasite powered or powered by external supplies The master needs this information to determine if the strong bus pullup should be used during temperature conversions To get this information the master can issue a Skip ROM CCh command followed by a Read Power Supply B4h command followed by a read time slot During the read time slot parasite powered DS1825s will pull the bus low and externally powered DS1825s will let the bus remain high If the bus is pulled low the master knows that it must supply the strong pullup on the 1 Wire bus during temperature conversions 6 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figu
24. rd pdf After every Search ROM cycle the bus master must return to Step 1 Initialization in the transaction sequence READ ROM 33h This command can only be used when there is one slave on the bus It allows the bus master to read the slave s 64 bit ROM code without using the Search ROM procedure If this command is used when there is more than one slave present on the bus a data collision will occur when all the slaves attempt to respond at the same time MATCH ROM 55h The match ROM command followed by a 64 bit ROM code sequence allows the bus master to address a specific slave device on a multidrop or single drop bus Only the slave that exactly matches the 64 bit ROM code sequence will respond to the function command issued by the master all other slaves on the bus will wait for a reset pulse SKIP ROM CCh The master can use this command to address all devices on the bus simultaneously without sending out any ROM code information For example the master can make all DS1825s 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 will cause a data collision on the bu
25. re 4 SUPPLYING THE PARASITE POWERED DS1825 DURING TEMPERATURE CONVERSIONS DS1825 Micro processor To Other 1 Wire Devices DS1825 Vpp External Supply Micro GND DQ Vrp processor To Other 1 Wire Bus 1 Wire Devices 64 BIT LASERED ROM CODE Each DS1825 contains a unique 64 bit code see Figure 6 stored in ROM The least significant 8 bits of the ROM code contain the DS1825 s 1 Wire family code 3Bh 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 DS1825 to operate as a 1 Wire device using the protocol detailed in the 1 Wire BUS SYSTEM section of this data sheet Figure 6 64 BIT LASERED ROM CODE 8 BIT CRC 48 BIT SERIAL NUMBER 8 BIT FAMILY CODE 3Bh MSB LSB MSB LSB MSB LSB MEMORY The DS1825 s memory is organized as shown in Figure 7 The memory consists of an SRAM scratchpad with NV EEPROM storage for the high and low alarm trigger registers T4 and T and configuration register Note that if the DS1825 alarm function is not used the Ty and T registers can serve as general purpose memory All memory commands are described in detail in the DS1825 FUNCTION COMMANDS section Byte 0 and byte 1 of the scratchpad conta
26. rom EEPROM to the scratchpad at any time using the Recall E B8h command The master can issue read time slots following the Recall E command and the DS1825 will indicate the status of the recall by transmitting O while the recall is in progress and 1 when the recall is done Figure 7 DS1825 MEMORY MAP SCRATCHPAD Power up State Temperature LSB 50h 85 C Temperature MSB 05h EEPROM Tu Register or User Byte 1 Tu Register or User Byte 1 T Register or User Byte 2 gt T Register or User Byte 2 Configuration Register t Configuration Register Reserved Reserved Reserved CRC Lower four bits of Configuration Register are hardwired through ADO AD3 CONFIGURATION REGISTER Byte 4 of the scratchpad memory is the configuration register as shown in Figure 8 The configuration register allows the user to set the conversion resolution using the RO and R1 bits and read the programmed value of the address pins The conversion resolution power up default is RO 1 and R1 1 12 bit resolution Table 4 shows the resolution configuration settings and maximum conversion time Note that there is a direct tradeoff between resolution and conversion time ADO AD3 bits report the pin programmed location information and are sampled at power up In Parasite Power mode the address pins must be connected to DQ or GND and in Vpp powered mode the address pins must be connected
27. s if there is more than one slave since multiple devices will attempt to transmit data simultaneously ALARM SEARCH ECh The operation of this command is identical to the operation of the Search ROM command except that only slaves with a set alarm flag will respond This command allows the master device to determine if any DS1825s 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 Refer to the OPERATION ALARM SIGNALING section for an explanation of alarm flag operation DS1825 FUNCTION COMMANDS After the bus master has used a ROM command to address the DS1825 with which it wishes to communicate the master can issue one of the DS1825 function commands These commands allow the master to write to and read from the DS1825 s scratchpad memory initiate temperature conversions and determine the power supply mode The DS1825 function commands which are described below are summarized in Table 5 and illustrated by the flowchart in Figure 12 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 DS1825 returns to its low power idle state If the device is being used in parasite power mode within 10us max af
28. sence DS1825s respond with presence pulse Master issues Search ROM command and builds TX FOh Crossreference Table TX Reset Master issues reset pulse RX Presence DS1825s respond with presence pulse TX 55h Master issues Match ROM command for desired address TX 64 bit ROM code Master sends DS1825 ROM code TX 44h Master issues Convert T command TX DQ line held high by Master applies strong pullup to DQ for the duration of the strong pullup conversion tcov TX Reset Master issues reset pulse RX Presence DS1825s respond with presence pulse TX 55h Master issues Match ROM command TX 64 bit ROM code Master sends DS1825 ROM code TX BEh Master issues Read Scratchpad command Master reads entire scratchpad including CRC The master then recalculates the CRC of the first eight data bytes from the RX 9 data bytes 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 18 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID Figure 18 TYPICAL PERFORMANCE CURVE o g S9 D t o o a o o L o a 2 e E Ww Temperature Degrees Centigrade Figure 19 TIMING DIAGRAMS 1 WIRE WRITE ZERO TIME SLOT START OF NEXT CYCLE 1 WIRE READ ZERO TIME SLOT START OF NEXT CYCLE 1 WIRE RESET PULSE RESET PULSE FROM HOST tastL 1 WIRE PRESENCE DETECT PRESENCE DETECT
29. side buildings equipment or machinery and process monitoring and control systems ABSOLUTE MAXIMUM RATINGS Voltage on Any Pin Relative to Ground 0 5V to 6 0V Operating Temperature Range 55 C to 125 C Storage Temperature Range 55 C to 125C Solder Dip Temperature 10s 260 C Reflow Oven Temperature 220 C 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 DC ELECTRICAL CHARACTERISTICS 55 C to 125 C Vpp 3 0V to 3 7V PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES Supply Voltage Vpp Local Power 3 0 3 7 V 1 Parasite Power 3 0 3 7 Pullup Supply Voltage Veu Local Power 3 0 Voo V 1 2 10 C to 85 C 0 5 C Thermometer Error TERR 55 C to 125 C 2 C 3 Programming Resistor ADO AD3 Recm 9 1g ES 12 DQ Input Logic Low Vii po 0 3 0 7 V 1 4 5 Local Power 2 2 The lower of DQ Input Logic High Vis e v 1 6 Parasite Power 3 0 Von 0 3 Sink Current IL Vio 0 4V 4 0 mA 1 Standby Current Ipps 500 1000 nA 7 8 Active Current lop Vpp 3 7V 0 65 1 5 mA 9 DQ Input Current IDa 5 pA 10 Drift 0 2 C 11 NOTES as All voltages are referenced to ground 2 The Pullup Supply Voltage specification assumes that the pullu
30. ter this command is issued the master must enable a strong pullup on the 1 Wire bus for the duration of the conversion tcony as described in the POWERING THE DS1825 section If the DS1825 is powered by an external supply the master can issue read time slots after the Convert T command and the DS1825 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done In parasite power mode this notification technique cannot be used since the bus is pulled high by the strong pullup during the conversion WRITE SCRATCHPAD 4Eh This command allows the master to write 3 bytes of data to the DS1825 s scratchpad The first data byte is written into the Ty register byte 2 of the scratchpad the second byte is written into the T 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 iButton is a registered trademark of Dallas Semiconductor 11 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID 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 O and continues through the scratchpad until the 9 byte byte 8 CRC is read The master may issue a reset to terminate reading at any time if onl
31. the 1 Wire SIGNALING section 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 DS1825 function command A flowchart for operation of the ROM commands is shown in Figure 11 10 of 21 DS1825 Programmable Resolution 1 Wire Digital Thermometer With 4 Bit ID SEARCH ROM FOh 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 of the slave devices If there is only one slave on the bus the simpler Read ROM command see below can be used in place of the Search ROM process For a detailed explanation of the Search ROM procedure refer to the iButton Book of Standards at www ibutton com ibuttons standa
32. ution of the temperature sensor is user configurable to 9 10 11 or 12 bits corresponding to increments of 0 5 C 0 25 C 0 125 C and 0 0625 C respectively The default resolution at power up is 12 bit The DS1825 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 12 bit temperature register in the scratchpad memory and the DS1825 returns to its idle state If the DS1825 is powered by an external supply the master can issue read time slots see the 1 Wire BUS SYSTEM section after the Convert T command and the DS1825 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done If the DS1825 is powered with parasite power this notification technique cannot be used since the bus must be pulled high by a strong pullup during the entire temperature conversion The bus requirements for parasite power are explained in detail in the POWERING THE DS1825 section of this data sheet The DS1825 output temperature data is calibrated in degrees centigrade 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 Figure 2 The sign bits S indicate if the temperature is positive or negative for positive
33. y part of the scratchpad data is needed COPY SCRATCHPAD 48h This command copies the contents of the scratchpad Ty T and configuration registers bytes 2 3 and 4 to EEPROM If the device is being used in parasite power mode within 10us 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 POWERING THE DS1825 section RECALL E B8h This command recalls the alarm trigger values Ty and T 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 E command and the DS1825 will indicate the status of the recall by transmitting O 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 READ POWER SUPPLY B4h The master device issues this command followed by a read time slot to determine if any DS1825s on the bus are using parasite power During the read time slot parasite powered DS1825s will pull the bus low and externally powered DS1825s will let the bus remain high Refer to the POWERING THE DS1825 section for usage information for this command Table 5 D81825 FUNCTION COMMAND SET FX 1 Wire Bus Activity Command Description Protocol Atter Command is
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