DS1822 Maxim Integrated Products, DS1822 Datasheet
DS1822
Specifications of DS1822
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DS1822 Summary of contents
Page 1
... Each DS1822 has a unique 64-bit serial code, which allows multiple DS1822s to function on the 1-Wire bus; thus simple to use one microprocessor to control many DS1822s distributed over a large area. Applications that can benefit from this feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment or machinery, and process monitoring and control systems ...
Page 2
... The control line requires a weak pullup resistor since all devices are linked to the bus via a 3-state or open-drain port (the DQ pin in the case of the DS1822). In this bus system, the microprocessor (the master device) identifies and addresses devices on the bus using each device’s unique 64-bit code. ...
Page 3
... DS1822 BLOCK DIAGRAM Figure PARASITE POWER 4.7K CIRCUIT DQ INTERNAL V GND 64-BIT ROM DD AND 1-wire PORT POWER SUPPLY SENSE DS1822 MEMORY CONTROL LOGIC TEMPERATURE SENSOR ALARM HIGH TRIGGER (T REGISTER (EEPROM) SCRATCHPAD ALARM LOW TRIGGER (T REGISTER (EEPROM) CONFIGURATION REGISTER (EEPROM) 8-BIT CRC GENERATOR ...
Page 4
... DS1822 returns to its idle state. If the DS1822 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 DS1822 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done ...
Page 5
... DS1822’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via the DQ pin when the bus is high. The stolen charge powers the DS1822 while the bus is high, and some of the charge is stored on the parasite power capacitor (C ...
Page 6
... During the read time slot, parasite powered DS1822s will pull the bus low, and externally powered DS1822s 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. ...
Page 7
... 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 DS1822 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 8
... The CRCs provide the bus master with a method of data validation when data is read from the DS1822. 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 the scratchpad CRC (for scratchpad reads) ...
Page 9
... BUS SYSTEM The 1-Wire bus system uses a single bus master to control one or more slave devices. The DS1822 is always a slave. When there is only one slave on the bus, the system is referred “single-drop” system; the system is “multidrop” if there are multiple slaves on the bus. ...
Page 10
... The presence pulse lets the bus master know that slave devices (such as the DS1822) 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
... DS1822 FUNCTION COMMANDS After the bus master has used a ROM command to address the DS1822 with which it wishes to communicate, the master can issue one of the DS1822 function commands. These commands allow the master to write to and read from the DS1822’s scratchpad memory, initiate temperature conversions and determine the power supply mode ...
Page 12
... READ POWER SUPPLY [B4h] The master device issues this command followed by a read time slot to determine if any DS1822s on the bus are using parasite power. During the read time slot, parasite powered DS1822s will pull the bus low, and externally powered DS1822s will let the bus remain high. Refer to the POWERING THE DS1822 section for usage information for this command ...
Page 13
... BIT BIT 0 BIT 0 MATCH? MATCH DS1822 T BIT 1 X MASTER T X DS1822 T BIT 1 X BIT 1 MASTER T BIT BIT 1 BIT 1 MATCH? MATCH DS1822 T BIT 63 X MASTER T DS1822 T BIT BIT 63 MASTER T BIT BIT 63 BIT 63 MATCH? MATCH MASTER T X FUNCTION COMMAND (FIGURE 12 CCh ECh N N SKIP ROM ...
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... DS1822 FUNCTION COMMANDS FLOW CHART Figure 12 44h MASTER T CONVERT X FUNCTION TEMPERATURE COMMAND ? Y N PARASITE POWER ? DS1822 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” MASTER ENABLES ...
Page 15
... 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 DS1822 and a Write 0 time slot to write a logic 0 to the DS1822. All write time slots must be a minimum of 60μs in duration with a minimum of a 1μs recovery time between individual write slots ...
Page 16
... DS1822 will begin transmitting bus. The DS1822 transmits leaving the bus high and transmits pulling the bus low. When transmitting a 0, the DS1822 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 ...
Page 17
... DS1822 is valid for 15μs after the falling edge that initiated the read time slot. Therefore, the master must release the bus and then sample the bus state within 15μs from the start of the slot. Figure 15 illustrates that the sum of T Figure 16 shows that system timing margin is maximized by keeping T and by locating the master sample time during read time slots towards the end of the 15μ ...
Page 18
... TX 64-bit ROM code data bytes DS1822 OPERATION EXAMPLE 2 In this example there is only one DS1822 on the bus and it is using parasite power. The master writes to the and configuration registers in the DS1822 scratchpad and then reads the scratchpad and H L recalculates the CRC to verify the data. The master then copies the scratchpad contents to EEPROM. ...
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... V =0.4V 4.0 I/O 750 V = ±0 order to meet the PU_ACTUAL PU_IDEAL 3.0V to 5.5V) DD MAX UNITS NOTES +5 ±2 °C ±3 +0 The lower 1000 nA 1.5 mA µA °C spec of the DS1822, the actual IH . TRANSISTOR may have to be ILMAX = 5.5V. DS1822 ...
Page 20
... SLOT t REC r LOW0 t LOW1 t RDV t RSTH t RSTL t PDHIGH t PDLOW C IN/OUT > 960μs, a power on reset may occur. RSTL DS1822 Typical Performance Curve +3s Error Mean Error -3s Error Temperature (° 3.0V to 5.5V) DD MIN TYP MAX 2 10 50k 10 = 3.0V to 5.5V) DD MIN TYP MAX UNITS 93.75 ms 187 ...
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... TIMING DIAGRAMS Figure DS1822 ...