外文翻译.docx

1、外文翻译外文翻译Programmable Resolution1-Wire Digital Thermometer FEATURES_Unique 1-WireTM interface requires only oneport pin for communication_.Multidrop capability simplifies distributedtemperature sensing applications_ Requires no external components_ Can be powered from data line. Power supplyrange is

2、3.0V to 5.5V_ Zero standby power required_ Measures temperatures from -55C to+125C. Fahrenheit equivalent is -67F to+257F_ C0.5 accuracy from -10C to +85C_ Thermometer resolution is programmablefrom 9 to 12 bits_ Converts 12-bit temperature to digital word in750 ms (max.)_ User-definable, nonvolatil

3、e temperature alarmsettings_ Alarm search command identifies andaddresses devices whose temperature is outside of programmed limits (temperature alarm condition)_ Applications include thermostatic controls, industrial systems, consumer products,thermometers, or any thermally sensitive systemPIN DESC

4、RIPTIONGND - GroundDQ - Data In/OutVDD - Power Supply VoltageNC - No ConnectDESCRIPTIONThe 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

5、one wire (and ground) 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,

6、 multiple DS18B20s can exist on the same 1-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.

7、DETAILED PIN DESCRIPTION Table 1DS18B20Z (8-pin 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 components of the DS18B20. The DS18B20 has four main data components: 1) 64-bit lasered ROM, 2) temperature se

8、nsor, 3) nonvolatile temperature alarm triggers 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 du

9、ring the low times of the 1-Wire line until it returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may also be powered from an external 3V - 5.5V supply. Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control functions wi

10、ll not be available 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 singl

11、e out a specific device 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 o

12、f the six memory and 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

13、the scratchpad memory. 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

14、 temperature to digital 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.DS18B20 3 of 26 DS18B20 BLOCK DIAGRAM Figure 1PARASITE POWERThe b

15、lock diagram (Figure 1) shows the parasite-powered 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 “1-Wire Bus System”). The advantages of parasite

16、 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

17、line when a temperature conversion is taking place. Since the operating 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

18、. 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 pullup 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 th

19、e DQ line directly to the power supply as shown in Figure 2. The DQ line must be switched over to the strong pullupwithin 10 s maximum after issuing any protocol that involves copying to the E2 memory or initiatestemperature conversions. This allows other data traffic on the 1-Wire bus during the co

20、nversion time. In addition, any number ofDS18B20s may be placed on the 1-Wire bus, and if they all use external power, they may all simultaneously perform temperature conversions by issuing the Skip ROM command and then issuing the Convert T command. Note that as long as the external power supply is

21、 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 likely, it is strongly r

22、ecommended 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 determine if any DS18B20s

23、 are on the bus which require the strong pullup 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 send back a “1” if it

24、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 TEMPERATURECONVERSION Fi

25、gure 2USING VDD TO SUPPLY TEMPERATURE CONVERSION CURRENT Figure 3OPERATION - MEASURING TEMPERATUREThe core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the DS18B20 is configurable (9, 10, 11, or 12 bits), with 12-bit readings the factory C,C, 0.25defaul

26、t state. This equates to a temperature resolution of 0.5 C. Following the issuance of the Convert T 44h command, aC, or 0.06250.125 temperature conversion is performed and the thermal data is stored in the scratchpad memory in a 16-bit, sign-extended twos complement format. The temperature informati

27、on can be retrieved over the 1-Wire interface by issuing a Read Scratchpad BEh command once the conversion has been performed. The data is transferred over the 1-Wire bus, LSB first. TheMSB of the temperature register contains the “sign” (S) bit, denoting whether the temperature is positive or negat

28、ive. Table 2 describes the exact relationship of output data to measured temperature. The table assumes 12-bit resolution. If the DS18B20 is configured for a lower resolution, insignificant bits will contain zeros. For Fahrenheit usage, a lookup table or conversion routine must be used.Temperature/D

29、ata Relationships Table 2Configuration RegisterThe fifth byte of the scratchpad memory is the configuration register.It contains information which will be used by the device to determine the resolution of the temperature todigital conversion. The bits are organized as shown in Figure 7.DS18B20 CONFI

30、GURATION REGISTER Figure 7Bits 0-4 are dont cares on a write but will always read out “1”. Bit 7 is a dont care on a write but will always read out “0”. R0, R1: Thermometer resolution bits. Table 3 below defines the resolution of the digital thermometer, based on the settings of these two bits. Ther

31、e is a direct tradeoff between resolution and conversion time, as depicted in the AC Electrical Characteristics. The factory default of these EEPROM bits is R0=1 and R1=1 (12-bit conversions).Thermometer Resolution Configuration Table 3DS18B20 MEMORY MAP Figure 81-WIRE BUS SYSTEMThe 1-Wire bus is a

32、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, transaction sequence, and 1-Wire signaling (signal types and timing).HARDWARE CONFIGURATIONThe 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open drain or 3-state outputs. The 1-Wire port of the DS18B20 (DQ pin) is open