【正文】 品系列編碼，唯一的48位序列號，以及8位的CRC?？偩€主機在ROM的每一位上完成這一簡單的三步過程。這表示連接著的器件ROM數(shù)據(jù)的第三位都是1數(shù)據(jù)位和0數(shù)據(jù)位。FThermometer resolution is programmable from 9 to 12 bitsConverts 12bit temperature to digital word in 750 ms (max.)Userdefinable, nonvolatile temperature alarm settingsAlarm search mand identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition)Applications include thermostatic controls, industrial systems, consumer products,thermometers, or any thermally sensitivesystem.PIN ASSIGNMENTPIN DESCRIPTIONGND GroundDQ Data In/OutVDD Power Supply VoltageNC No ConnectDETAILED PIN DESCRIPTION OVERVIEWThe block diagram of Figure 1 shows the major ponents of the DS18B20. The DS18B20 has four main data ponents: 1) 64bit lasered ROM, 2) temperature sensor, 3) nonvolatile temperature alarm triggers TH and TL. The device derives its power from the 1Wire munication line by storing energy on an internal capacitor during periods of time when the signal line is high and continues to operate off this power source during the low times of the 1Wire line until it returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may also be powered from an external 3 volt volt supply.DS18B20 BLOCK DIAGRAM Figure 1Communication to the DS18B20 is via a 1Wire port. With the 1Wire port, the memory and control functions will not be available before the ROM function protocol has been established. The master must first provide one of five ROM function mands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm Search. These mands operate on the 64bit lasered ROM portion of eachdevice and can single out a specific device if many are present on the 1Wire line as well as indicate to the bus master how many and what types of devices are present. After a ROM function sequence has been successfully executed, the memory and control functions are accessible and the master may then provide any one of the six memory and control function mands. One control function mand instructs the DS18B20 to perform a temperature measurement. The result of this measurement will be placed in the DS18B20’s scratchpad memory, and may be read by issuing a memory function mand which reads the contents of the scratchpad memory. The temperature alarm triggers TH and TL consist of 1 byte EEPROM each. If the alarm search mand is not applied to the DS18B20, these registers may be used as general purpose user memory. The scratchpad also contains a configuration byte to set the desired resolution of the temperature to digital conversion. Writing TH, TL, and the configuration byte is done using a memory function mand. Read access to these registers is through the scratchpad. All data is read and written least significant bit first.1WIRE BUS SYSTEMThe 1Wire bus is a system which has a single bus master and one or more slaves. The DS18B20 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware configuration, transac