【正文】 needs to be connected from a central microprocessor to a DS18B20. Power for reading, writing, and performing temperature conversions can be derived from the data line itself with no need for an external power source.Because each DS18B20 contains a unique silicon serial number, multiple DS18B20s can exist on the same 1Wire bus. This allows for placing temperature sensors in many different places. Applications where this feature is useful include HVAC environmental controls, sensing temperatures inside buildings, equipment or machinery, and process monitoring and control. FEATURES(1) Unique 1WireTM interface requires only one port pin for munication(2) Multidrop capability simplifies distributed temperature sensing applications(3) Requires no external ponents(4) Can be powered from data line. Power supply range is to (5) Zero standby power required(6) Measures temperatures from 55176。C to+125176。C. Fahrenheit equivalent is 67176。F to+257176。F(7) 176。C accuracy from 10176。C to +85176。C(8) Thermometer resolution is programmable from 9 to 12 bits(9) Converts 12bit temperature to digital word in 750 ms (max.)(10) Userdefinable, nonvolatile temperature alarm settings(11) Alarm search mand identifies and addresses devices whose temperature is outside of programmed limits (temperature alarm condition)(12) Applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system PIN ASSIGNMENTDETAILED PIN DESCRIPTION Table 1DS18B20Z (8pin SOIC) and DS18P20P (TSOC): All pins not specified in this table are not to be connected. 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, and 4) a configuration register. 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 bepowered from an external 3V 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 each device 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. PARASITE POWERThe block diagram (Figure 1) shows the parasitepowered circuitry. This circuitry “steals” power whenever the DQ or VDD pins are high. DQ will provide sufficient power as long as the specified timing and voltage requirements are met (see the section titled “1Wire Bus System”). The advantages of parasite power are twofold: 1) by parasiting off this pin, no local power source is needed for remote sensing of temperature, and 2) the ROM may be read in absence of normal power.In order for the DS18B20 to be able to perform accurate temperature conversions, sufficient power must be provided over the DQ line when a temperature conversion is taking place. Since the operating current of the DS18B20 is up to mA, the DQ line will not have sufficient drive due to the 5k pullup resistor. This problem is particularly acute if several DS18B20s are on the same DQ and attempting to convert simultaneously.There are two ways to assure that the DS18B20 has sufficient supply current during its active conversion cycle. The first is to provide a strong pull up on the DQ line whenever temperature conversions or copies to the E2 memory are taking place. This may be acplished by using a MOSFET to pull the DQ line directly to the power supply as shown in Figure 2. The DQ line must be switched over to the strong pull up within 10 s maximum after issuing any protocol that involves copying to the E2 memory or initiates temperature conversions. When using the parasite power mode, the VDD pin must be tied to ground.Another method of supplying current to the DS18B20 is through the use of an external power supply tied to the VDD pin, as shown in Figure 3. The advantage to this is that the strong pullup is not required on the DQ line, and the bus master need not be tied up holding that line high during temperature allows other data traffic on the 1Wire bus during the conversion time. In addition, any number of DS18B20s may be placed on the 1Wire bus, and if they all use external power, they may all imultaneously perform temperature conversions by issuing the Skip ROM mand and then issuing the Convert T mand. Note that as long as the e