DS18B20数字式温度传感器毕业论文中英文资料外文翻译文献.doc

1、外文翻译（原文） 中英文资料外文翻译文献 The introduction to The DS18B201. DESCRIPTION The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with nonvolatile user programmable upper and lower trigger points. The DS18B20 communicates over a 1-Wire bus that by

2、 definition requires only one data line for communication with a central microprocessor. It has an operating temperature range of -55C to +125C and is accurate to 0.5C over the range of -10C to +85C. In addition, the DS18B20 can derive power directly from the data line (“parasite power”), eliminatin

3、g the need for an external power supply. Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-Wire bus. Thus, it is simple to use one microprocessor to control many DS18B20s distributed over a large area. Applications that can benefit from this featu

4、re include HVAC environmental controls, temperature monitoring systems inside buildings, equipment, or machinery, and process monitoring and control systems.2.FEATURESl Unique 1-Wire Interface Requires Only One Port Pin for Communicationl Each Device has a Unique 64-Bit Serial Code Stored in an On-B

5、oard ROMl Multi-drop Capability Simplifies Distributed Temperature-Sensing Applicationsl Requires No External Componentsl Can Be Powered from Data Line; Power Supply Range is 3.0V to 5.5V l Measures Temperatures from -55C to +125C (-67F to +257F)l 0.5C Accuracy from -10C to +85Cl Thermometer Resolut

6、ion is User Selectable from 9 to 12 Bitsl Converts Temperature to 12-Bit Digital Word in 750ms (Max)l User-Definable Nonvolatile (NV) Alarm Settingsl Alarm Search Command Identifies and Addresses Devices Whose Temperature is Outside Programmed Limitsl Software Compatible with the DS1822l Application

7、s Include Thermostatic Controls, Industrial Systems, Consumer Products, Thermometers, or Any Thermally Sensitive System3.OVERVIEWFigure 1 shows a block diagram of the DS18B20, and pin descriptions are given in the Pin Description table. The 64-bit ROM stores the devices unique serial code. The scrat

8、chpad memory contains the 2-byte temperature register that stores the digital output from the temperature sensor. In addition, the scratchpad provides access to the 1-byte upper and lower alarm trigger registers (TH and TL) and the 1-byte configuration register. The configuration register allows the

9、 user to set the resolution of the temperature to-digital conversion to 9, 10, 11, or 12 bits. The TH, TL, and configuration registers are nonvolatile (EEPROM), so they will retain data when the device is powered down.The DS18B20 uses Maxims exclusive 1-Wire bus protocol that implements bus communic

10、ation using one control signal. The control line requires a weak pull up resistor since all devices are linked to the bus via a 3-state or open-drain port (the DQ pin in the case of the DS18B20). In this bus system, the microprocessor (the master device) identifies and addresses devices on the bus u

11、sing each devices unique 64-bit code. Because each device has a unique code, the number of devices that can be addressed on one DS18B20 bus is virtually unlimited. The 1-Wire bus protocol, including detailed explanations of the commands and “time slots,” is covered in the 1-Wire Bus System section.A

12、nother feature of the DS18B20 is the ability to operate without an external power supply. Power is instead supplied through the 1-Wire pull up resistor via the DQ pin when the bus is high. The high bus signal also charges an internal capacitor (CPP), which then supplies power to the device when the

13、bus is low. This method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an alternative, the DS18B20 may also be powered by an external supply on VDD. Figure 1.DS18B20 Block Diagram4.OPERATIONMEASURING TEMPERATURThe core functionality of the DS18B20 is its direct-to-digit

14、al temperature sensor. The resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5C, 0.25C, 0.125C, and 0.0625C, respectively. The default resolution at power-up is 12-bit. The DS18B20 powers up in a low-power idle state. To initiate a t

15、emperature measurement and A-to-D conversion, the master must issue a Convert T 44h command. Following the conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its idle state. If the DS18B20 is powered by an external

16、supply, the master can issue “read time slots” (see the 1-Wire Bus System section) after the Convert T command and the DS18B20 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done. If the DS18B20 is powered with parasite power, this notific

17、ation technique cannot be used since the bus must be pulled high by a strong pull up during the entire temperature conversion. The DS18B20 output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, a lookup table or conversion routine must be used. The temperature data is

18、 stored as a 16-bit sign-extended twos complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the DS18B20 is configured for 12-bit resolution, all bits in the t

19、emperature register will contain valid data. For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and the corresponding temperature reading for 12-bit resol

20、ution conversions. bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0LS Byte232221202-12-22-32-4 bit15 bit14 bit13 bit12 bit11 bit10 bit9 bit8MS ByteSSSSS262524Figure 2.Temperature Register FormatTEMPERATURE DIGITAL OUTPUT (BINARY) DIGITAL OUTPUT (HEX) +1250000 0111 1101 000007D0H+25.06250000 0001 1001 0001019

21、1H00000 0000 0000 00000000H-25.06251111 1110 0110 1111FE6FH-551111 1100 1001 0000FC90HTable 1.Temperature/Data Relationship5.64-BIT LASERED ROM CODEEach DS18B20 contains a unique 64bit code (see Figure 3) stored in ROM. The least significant 8 bits of the ROM code contain the DS18B20s 1-Wire family

22、code: 28h. The next 48 bits contain a unique serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is calculated from the first 56 bits of the ROM code. The 64-bit ROM code and associated ROM function control logic allow the DS18B20 to operate as a 1-Wire devic

23、e using the protocol detailed in the 1-Wire Bus System section.8-BIT CRC48-BIT SERIAL NUMBER8-BIT FAMILY CODE MSB LSB MSB LSB MSBFigure 3.64-Bit Lasered ROM Code6.MEMORYThe DS18B20s memory is organized as shown in Figure 4. The memory consists of an SRAM scratchpad with nonvolatile EEPROM storage fo

24、r the high and low alarm trigger registers (TH and TL) and configuration register. Note that if the DS18B20 alarm function is not used, the TH and TL registers can serve as general-purpose memory. Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register, respective

25、ly. These bytes are read-only. Bytes 2 and 3 provide access to TH and TL registers. Byte 4 contains the configuration register data. Bytes 5, 6, and 7 are reserved for internal use by the device and cannot be overwritten. Byte 8 of the scratchpad is read-only and contains the CRC code for bytes 0 th

26、rough 7 of the scratchpad. The DS18B20 generates this CRC using the method described in the CRC Generation section.Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad 4Eh command; the data must be transmitted to the DS18B20 starting with the least significant bit of byt

27、e 2. To verify data integrity, the scratchpad can be read (using the Read Scratchpad BEh command) after the data is written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least significant bit of byte 0. To transfer the TH, TL and configuration data from the

28、scratchpad to EEPROM, the master must issue the Copy Scratchpad 48h command.Byte0Temperature LSBByte1Temperature MSBByte2TH Register for high temperatureByte3TL Register for low temperatureByte4Configuration RegisterByte5Reserved（FFH）Byte6Reserved（OCH）Byte7Reserved（IOH）Byte8Cyclic Redundancy Checks（

29、CRC） Figure 4.DS18B20 Memory Map7.CONFIGURATION REGISTERByte 4 of the scratchpad memory contains the configuration register, which is organized as illustrated in Figure 5. The user can set the conversion resolution of the DS18B20 using the R0 and R1 bits in this register as shown in Table 2. The pow

30、er-up default of these bits is R0 = 1 and R1 = 1 (12-bit resolution). Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits 0 to 4 in the configuration register are reserved for internal use by the device and cannot be overwritten. BIT7 BIT6 BIT5 BIT4 BIT3 BIT2

31、BIT1 BIT0TMR1R011111 Figure 5.Configuration RegisterR0R1RESOLUTION(BITS)MAX CONVERSION TIME00110101910111293.75ms187.5ms375ms750ms Table 2.Thermometer Resolution Configuration8.1-WIRE BUS SYSTEMThe 1-Wire bus system uses a single bus master to control one or more slave devices. The DS18B20 is always

32、 a slave. When there is only one slave on the bus, the system is referred to as a “single-drop” system; the system is “multi-drop” if there are multiple slaves on the bus. All data and commands are transmitted least significant bit first over the 1-Wire bus. The following discussion of the 1-Wire bu

33、s system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing).9.TRANSACTION SEQUENCEThe transaction sequence for accessing the DS18B20 is as follows:Step 1. Initialization Step 2. ROM Command (followed by any required data exc

34、hange)Step 3. DS18B20 Function Command (followed by any required data exchange)It is very important to follow this sequence every time the DS18B20 is accessed, as the DS18B20 will not respond if any steps in the sequence are missing or out of order. Exceptions to this rule are the Search ROM F0h and

35、 Alarm Search ECh commands. After issuing either of these ROM commands, the master must return to Step 1 in the sequence.（1）INITIALIZATIONAll transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master foll

36、owed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that slave devices (such as the DS18B20) are on the bus and are ready to operate. （2）ROM COMMANDSAfter the bus master has detected a presence pulse, it can issue a ROM command. These commands operate o

37、n the unique 64-bit ROM codes of each slave device and allow the master to single out a specific device if many are present on the 1-Wire bus. These commands also allow the master to determine how many and what types of devices are present on the bus or if any device has experienced an alarm conditi

38、on. There are five ROM commands, and each command is 8 bits long. The master device must issue an appropriate ROM command before issuing a DS18B20 function command. 1.SEARCH ROM F0hWhen a system is initially powered up, the master must identify the ROM codes of all slave devices on the bus, which al

39、lows the master to determine the number of slaves and their device types. The master learns the ROM codes through a process of elimination that requires the master to perform a Search ROM cycle (i.e., Search ROM command followed by data exchange) as many times as necessary to identify all of the sla

40、ve devices. If there is only one slave on the bus, the simpler Read ROM command can be used in place of the Search ROM process. 2.READ ROM 33hThis command can only be used when there is one slave on the bus. It allows the bus master to read the slaves 64-bit ROM code without using the Search ROM pro

41、cedure. If this command is used when there is more than one slave present on the bus, a data collision will occur when all the slaves attempt to respond at the same time.3.MATCH ROM 55hThe match ROM command followed by a 64-bit ROM code sequence allows the bus master to address a specific slave devi

42、ce on a multi-drop or single-drop bus. Only the slave that exactly matches the 64-bit ROM code sequence will respond to the function command issued by the master; all other slaves on the bus will wait for a reset pulse.4.SKIP ROM CChThe master can use this command to address all devices on the bus s

43、imultaneously without sending out any ROM code information. For example, the master can make all DS18B20s on the bus perform simultaneous temperature conversions by issuing a Skip ROM command followed by a Convert T 44h command. Note that the Read Scratchpad BEh command can follow the Skip ROM comma

44、nd only if there is a single slave device on the bus. In this case, time is saved by allowing the master to read from the slave without sending the devices 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad command will cause a data collision on the bus if there is more than one slave

45、 since multiple devices will attempt to transmit data simultaneously.5.ALARM SEARCH EChThe operation of this command is identical to the operation of the Search ROM command except that only slaves with a set alarm flag will respond. This command allows the master device to determine if any DS18B20s

46、experienced an alarm condition during the most recent temperature conversion. After every Alarm Search cycle (i.e., Alarm Search command followed by data exchange), the bus master must return to Step 1 (Initialization) in the transaction sequence. （3）DS18B20 FUNCTION COMMANDS After the bus master ha

47、s used a ROM command to address the DS18B20 with which it wishes to communicate, the master can issue one of the DS18B20 function commands. These commands allow the master to write to and read from the DS18B20s scratchpad memory, initiate temperature conversions and determine the power supply mode. 1.CONVERT T 44hThis command initiates a single temperature conversion. Following the conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its low-power idle state. If the device is being used in parasite powe