DS18B20 数字温度计外文翻译.docx

1、DS18B20 数字温度计外文翻译外文资料原文DS18B201.1 DESCRIPTIONThe DS18B20 Digital Thermometer provides 9 to 12-bit (configurable) temperature readings which indicate the temperature of the device. Information is sent to/from the DS18B20 over a 1-Wire interface, so that only one wire (and ground) needs to be connecte

2、d 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 1-

3、Wire 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.1.2 FEATURES(1) Unique 1-WireTM interface r

4、equires only one port pin for communication(2) Multidrop capability simplifies distributed temperature sensing applications(3) Requires no external components(4) Can be powered from data line. Power supply range is 3.0V to 5.5V(5) Zero standby power required(6) Measures temperatures from -55C to+125

5、C. Fahrenheit equivalent is -67F to+257F(7) 0.5C accuracy from -10C to +85C(8) Thermometer resolution is programmable from 9 to 12 bits(9) Converts 12-bit temperature to digital word in 750 ms (max.)(10) User-definable, nonvolatile temperature alarm settings(11) Alarm search command identifies and a

6、ddresses 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 system1.3 PIN ASSIGNMENTDETAILED PIN DESCRIPTION Table 1DS18B20Z (8-pin SOI

7、C) and DS18P20P (TSOC): All pins not specified in this table are not to be connected.1.4 OVERVIEWThe block diagram of Figure 1 shows the major components of the DS18B20. The DS18B20 has four main data components: 1) 64-bit lasered ROM, 2) temperature sensor, 3) nonvolatile temperature alarm triggers

8、 TH and TL, and 4) a configuration register. The device derives its power from the 1-Wire communication 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 1-Wire line until it

9、returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may also bepowered from an external 3V - 5.5V supply.DS18B20 BLOCK DIAGRAM Figure 1Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control functions will not be available

10、 before the ROM function protocol has been established. The master must first provide one of five ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4)Skip ROM, or 5) Alarm Search. These commands operate on the 64-bit lasered ROM portion of each device and can single out a specific dev

11、ice if many are present on the 1-Wire 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

12、 control function commands. One control function command instructs the DS18B20 to perform a temperature measurement. The result of this measurement will be placed in the DS18B20s scratch-pad memory, and may be read by issuing a memory function command which reads the contents of the scratchpad memor

13、y. The temperature alarm triggers TH and TL consist of 1 byte EEPROM each. If the alarm search command 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 digi

14、tal conversion. Writing TH, TL,and the configuration byte is done using a memory function command. Read access to these registers is through the scratchpad. All data is read and written least significant bit first.1.5 PARASITE POWERThe block diagram (Figure 1) shows the parasite-powered circuitry. T

15、his 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 “1-Wire Bus System”). The advantages of parasite power are twofold: 1) by parasiting off this pin, no local pow

16、er 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 op

17、erating current of the DS18B20 is up to 1.5 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 su

18、pply 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 accomplished by using a MOSFET to pull the DQ line directly to the power supply as shown in Figure 2. The

19、 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 i

20、s 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 conversions.This allows other data traffic on the

21、1-Wire bus during the conversion time. In addition, any number of DS18B20s may be placed on the 1-Wire bus, and if they all use external power, they may all imultaneously perform temperature conversions by issuing the Skip ROM command and then issuing the Convert T command. Note that as long as the

22、external power supply is active, the GND pin may not be floating.The use of parasite power is not recommended above 100C, since it may not be able to sustain communications given the higher leakage currents the DS18B20 exhibits at these temperatures. For applications in which such temperatures are l

23、ikely, it is strongly recommended that VDD be applied to the DS18B20.For situations where the bus master does not know whether the DS18B20s on the bus are parasite powered or supplied with external VDD, a provision is made in the DS18B20 to signal the power supply scheme used. The bus master can det

24、ermine if any DS18B20s are on the bus which require the strong Pull up by sending a Skip ROM protocol, then issuing the read power supply command. After this command is issued, the master then issues read time slots. The DS18B20 will send back “0” on the 1-Wire bus if it is parasite powered; it will

25、 send back a “1” if it is powered from the VDD pin. If the master receives a “0”, it knows that it must supply the strong pullup on the DQ line during temperature conversions.See “Memory Command Functions” section for more detail on this command protocol.STRONG PULLUP FOR SUPPLYING DS18B20 DURING TE

26、MPERATURECONVERSION Figure 2USING VDD TO SUPPLY TEMPERATURE CONVERSION CURRENT Figure 31.6 OPERATION - ALARM SIGNALINGAfter the DS18B20 has performed a temperature conversion, the temperature value is compared to the trigger values stored in TH and TL. Since these registers are 8-bit only, bits 9-12

27、 are ignored for comparison. The most significant bit of TH or TL directly corresponds to the sign bit of the 16-bit temperature register. If the result of a temperature measurement is higher than TH or lower than TL, an alarm flag inside the device is set. This flag is updated with every temperatur

28、e measurement. As long as the alarm flag is set, the DS18B20 will respond to the alarm search command. This allows many DS18B20s to be connected in parallel doing simultaneous temperature measurements. If somewhere the temperature exceeds the limits, the alarming device(s) can be identified and read

29、 immediately without having to read non-alarming devices.1.7 64-BIT LASERED ROMEach DS18B20 contains a unique ROM code that is 64-bits long. The first 8 bits are a 1-Wire family code (DS18B20 code is 28h). The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. (

30、See Figure 4.) The 64-bit ROM and ROM Function Control section allow the DS18B20 to operate as a 1-Wire device and follow the 1-Wire protocol detailed in the section “1-Wire Bus System”. The functions required to control sections of the DS18B20 are not accessible until the ROM function protocol has

31、been satisfied. This protocol is described in the ROM function protocol flowchart (Figure 5). The 1-Wire bus master must first provide one of five ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm Search. After a ROM function sequence has been successfully exe

32、cuted, the functions specific to the DS18B20 are accessible and the bus master may then provide one of the six memory and control function commands.64-BIT LASERED ROM Figure 41.8 CRC GENERATIONThe DS18B20 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master can compute a CRC value from the first 56-bits of the 64-bit ROM and compare it to the value stored within the DS18B20 to determine if the ROM data has been received error-free by the bus master. The equivalent polynomial function of this CRC is: CRC = X8 + X5 + X4 + 1The DS18B20 als