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1、DS18B20 Programmable Resolution 1-Wire Digital Thermometer1、DS18B20 FEATURES(1) Unique 1-Wire interface requires only one Port pin for communication, requires no external components(2) Each device has a unique 64-bit serial code stored in an onboard ROM(3) Can be powered form data line .Power supply
2、 range is 3.0Vto 5.5V(4) Measures temperatures form -55C to +125C , 0.5C accuracy from -10C to +85 C(5) Thermometer resolution is user-selected from 9 to 12 bits(6) Converts temperature to 12-bit digital word in 750ms (max)(7) Alarm search command identifies and addresses devices whose temperature i
3、s outside of programmed limits (temperature alarm condition)(8) Available in 8-pin SOIC, and 3-bin TO -92 packages2、DS18B20 BLOCK DIAFRAMFigure 1 shows a block diagram of the DS18B20, The 64-bite ROM stores the devices serial code. The scratchpad memory cont-biyts temperature egister that stores the
4、 digital output from the temperature sensor. In addition, the scratchpad provides access to the 1-byte upper and lower alarm trigger register (TH and TL), and the 1-byte configuratuion register. The configuration register allows the user to set the resolution of the temperature-to-digital conversion
5、 to 9, 10, 11 or 12 bits. The TH,TL and configuration registers are nonvolatile(EEPROM), so they will retain data when the device is powered down.VD1Ll_POMSUPPYSENSEa64-BITEkOM .孙D Eire PortFigure 1 block diagram of the DS18B203、DS18B20 ROM COMMANDS(1) SEARCH ROM 0F0HWhen a system is initially power
6、ed 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 as many times as ne
7、cessary to identify all of the -biaROM? devices.(2) READ ROM 55HThis command can only be used when there is one slave on the bus. It allows the bus master to read the slave64-bit ROM code without using the Search ROM procedure. If this command is used when there is more than one slave present on the
8、 bus, a data collision will occur when all the slaves attempt to respond at the same time.(3) MATCH ROM 55HThe match ROM command followed by a 64-bit ROM code sequence allows the bus master to address a specific DS18B20 on a multidrop or single-drop bus. Only the DS18B20 that exactly matches the 64-
9、bitROM code sequence will respond to thefunction command issued by the master; all other slaves on the bus will wait for a reset pulse.(4) SKIP ROM 0CCHThe master can use this command to address all devices on the bus simultaneously without sending out any ROM code information. Note that the Read Sc
10、ratchpad 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 devices 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad command will cause a data collisi
11、on on the bus if there is more than one slave since multiple devices will attempt to transmit data simultaneously.(5) ALARM SEARCH 0ECHThe 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
12、 the master device to determine if any DS18B20s experienced an alarm condition during the most recent temperature conversion .Refer to the OPERATION-ALARM SIGNAING section for an explanation of alarm flag operation.(6) CONVERTT 44HThis command initiates a single temperature conversion. Following the
13、 conversion, the resulting thermal data is stored in the 2-bute temperature register in the scratchpad memory and the DS18B20 returns to its low-power idle state. If the device is being used in parasite power mode, within 10us after this command is issued the master must enable a strong pullup on th
14、e 1-Wire bus for the duration of the conversion as described in the POWERING THE DS18320 section. If the DS18B20 is powered by an external supply, the master can issue read time slots after the Convert T command and the DS18B20 will respond by transmitting a 0 while the temperature conversion is in
15、Progress and a 1 when the conversion is done. In parasite power mode this notification technique cannot be used since the bus1 is pulled high by the strong pullup during the conversion.(7) WRITE SCRACHPAD 4EHThis command allows the master to write 3 bytes of the data to the DS18B20s scratchpad. The
16、first data byte is writer into the TH register , the second byte is written into the TL register, and the third byte is written into the configuration register.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.(8) READ SCRACHPAD 0BEHThis command allows the master to read the contents of the scra
