DS1825 Maxim Integrated Products, DS1825 Datasheet
DS1825
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DS1825 Summary of contents
Page 1
... 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. ...
Page 2
... Inputs AD0-AD3 must be tied either High or Low. A "Low" connection to the GND terminal. A "High" connection varies with usage of the DS1825. When connected as a parasite powered sensor, a connection considered a High. When powered through the V pin, a connection High. If left floating, the input values are indeterminate and may be either logical "0" or logical "1." See DD Figures 20 and 21 for details ...
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AC ELECTRICAL CHARACTERISTICS: NV MEMORY PARAMETER NV Write Cycle Time EEPROM Writes EEPROM Data Retention AC ELECTRICAL CHARACTERISTICS PARAMETER Temperature Conversion Time Time to Strong Pullup On Time Slot Recovery Time Write 0 Low Time Write 1 Low Time Read ...
Page 4
... 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 ...
Page 5
... Figure 2). The sign bits (S) indicate if the temperature is positive or negative: for positive numbers and for negative numbers the DS1825 is configured for 12- bit resolution, all bits in the temperature register will contain valid data. For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1 and 0 are undefined ...
Page 6
... 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 ...
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... 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 ...
Page 8
... 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 ...
Page 9
... 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 0s. Additional information about the Dallas 1-Wire cyclic redundancy check is available in Application Note 27 entitled “ ...
Page 10
... 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 the 1-Wire SIGNALING section. ...
Page 11
... 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 T register (byte 2 of the scratchpad), the second byte is written into the T H byte is written into the configuration register (byte 4) ...
Page 12
... 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 ...
Page 13
... MATCH DS1825 T BIT 1 X MASTER T X DS1825 T BIT 1 X BIT 1 MASTER T BIT BIT 1 BIT 1 MATCH? MATCH DS1825 T BIT 63 X MASTER T DS1825 T BIT BIT 63 MASTER T BIT BIT 63 BIT 63 MATCH? MATCH MASTER T X FUNCTION COMMAND ...
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... Figure 12. DS1825 FUNCTION COMMANDS FLOW CHART 44h MASTER T CONVERT X FUNCTION TEMPERATURE COMMAND ? Y N PARASITE POWER ? DS1825 BEGINS CONVERSION DEVICE N CONVERTING TEMPERATURE ? Y MASTER MASTER R “0s” R “1s” B4h N READ POWER SUPPLY ? PARASITE POWERED ? MASTER MASTER R “1s” R “0s” ...
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... 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 Increment Counter Search all ROMIDs on bus & ...
Page 16
... 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 60ms in duration with a minimum of a types of write time slots are initiated by the master pulling the 1-Wire bus low (see Figure 14) ...
Page 17
... The DS1825 transmits leaving the bus high and transmits pulling the bus low. When transmitting a 0, the DS1825 will release the bus by the end of the time slot, and the bus will be pulled back to its high idle state by the pullup resister. Output data from the DS1825 is valid for 15ms after the falling edge that initiated the read time slot ...
Page 18
... 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 the data. MASTER MODE ...
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Figure 18. TYPICAL PERFORMANCE CURVE -1 Figure 19. TIMING DIAGRAMS 1 +3σ 0 -3σ - Temperature, Degrees Centigrade ...
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Figure 20. ADDRESS PROGRAMMING DIAGRAM, V 1-Wire Bus Note: AD0-AD3 cannot float, each pin must be tied to either V Location 0 DQ AD0 AD1 VDD VDD AD2 GND AD3 VDD Location 1 DQ AD0 AD1 VDD AD2 GND AD3 ...
Page 21
Figure 21. ADDRESS PROGRAMMING DIAGRAM, PARASITE POWERED 1-Wire Bus Note: AD0-AD3 cannot float, each pin must be tied to either V Location 0 DQ AD0 ADO = GND AD1 AD1 = GND VDD AD2 AD2 = GND GND AD3 AD3 ...