1、外文资料原文 DS18B20 1.1 DESCRIPTION The 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 connected from a centr
2、al 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-Wire bus. Thi
3、s 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 requires onl
4、y 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+125C. Fah
5、renheit equivalent is -67F to+257F (7) 0.5 C 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 system 1.3 PIN ASSIGNMENT DETAILED PIN DESCRIPTION Table 1 DS18B20Z (8-pin
7、 SOIC) and DS18P20P (TSOC): All pins not specified in this table are not to be connected. 1.4 OVERVIEW The 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 tr
8、iggers 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 unt
9、il 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. DS18B20 BLOCK DIAGRAM Figure 1 Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control functions will not be
10、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 single out a spe
11、cific 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 of the six m
12、emory 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 the scratch
13、pad 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 temperatur
14、e 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. 1.5 PARASITE POWER The block diagram (Figure 1) shows the parasite-powered
15、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 power are twofold: 1) by parasiting off this pin,
16、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.
17、 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. 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
