DS18B20数字温度计：1-Wire技术，可编程分辨率

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"DS18B20英文手册是关于一种具有1-Wire接口的数字温度计，该设备可实现程序化分辨率的温度测量，并适用于分布式温度传感应用。它只需要一个端口引脚进行通信，支持多滴配置。DS18B20无需外部组件即可工作，电源电压范围为3.0V到5.5V，且在待机时功耗为零。它可以测量-55°C到+125°C的温度，精度在-10°C到+85°C范围内可达±0.5°C。温度分辨率可在9到12位之间编程调整，并能在750毫秒内完成12位温度转换为数字值。此外，用户可定义非易失性温度报警设置，当温度超出预设限制时，报警搜索命令能识别并处理设备的报警状态。这种传感器广泛应用于恒温控制、工业系统、消费产品、温度计等各种对温度敏感的系统。" 详细说明： DS18B20是一款独特的1-Wire数字温度计，其主要特点在于其简洁的通信接口和灵活的性能。1-Wire接口使得只需一根数据线（DQ）就能实现与微控制器的双向通信，大大简化了布线和系统设计。同时，DS18B20具备多滴功能，能够在一条总线上连接多个设备，实现分布式温度监控。该传感器无需额外的外部元件，可以直接从数据线上获取电源，工作电压范围宽泛，适合多种应用场景。DS18B20在无操作时不会消耗任何电力，确保了高效节能。在温度测量方面，它的能力非常出色，能够测量从极低温(-55°C)到高温(+125°C)的范围，其精度在常用工作温度区间(-10°C至+85°C)达到了±0.5°C，确保了测量的准确性。 DS18B20的分辨率可通过编程设置，用户可以选择9位到12位的温度分辨率，以适应不同精度需求。转换速度非常快，最大不超过750毫秒，就能将温度转换成12位的数字值，这对于实时温度监测来说非常重要。此外，DS18B20还提供用户定义的非易失性温度报警设置，这意味着即使在断电后，这些设置也能被保存。一旦温度超出预设的上下限，通过报警搜索命令，系统可以快速定位并响应那些处于报警状态的设备，这在自动化控制和监控系统中非常实用。在实际应用中，DS18B20广泛用于恒温控制系统，如家庭和工业用的空调或加热系统；工业环境中的温度监测，如生产过程控制；以及各种消费产品，例如智能冰箱、烤箱等家用电器。此外，它还适用于各种需要精确温度读取的场合，如实验室设备、医疗设备以及环境监测系统。DS18B20凭借其卓越的性能和易用性，成为了温度测量领域的一个理想选择。

DS18B20

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64-BIT LASERED ROM

Each 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. (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 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 executed, the functions specific to the DS18B20 are accessible and the

bus master may then provide one of the six memory and control function commands.

CRC GENERATION

The 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 = X

+ X

+ 1

The DS18B20 also generates an 8-bit CRC value using the same polynomial function shown above and

provides this value to the bus master to validate the transfer of data bytes. In each case where a CRC is

used for data transfer validation, the bus master must calculate a CRC value using the polynomial

function given above and compare the calculated value to either the 8-bit CRC value stored in the 64-bit

ROM portion of the DS18B20 (for ROM reads) or the 8-bit CRC value computed within the DS18B20

(which is read as a ninth byte when the scratchpad is read). The comparison of CRC values and decision

to continue with an operation are determined entirely by the bus master. There is no circuitry inside the

DS18B20 that prevents a command sequence from proceeding if the CRC stored in or calculated by the

DS18B20 does not match the value generated by the bus master.

The 1-Wire CRC can be generated using a polynomial generator consisting of a shift register and XOR

gates as shown in Figure 6. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is

available in Application Note 27 entitled “Understanding and Using Cyclic Redundancy Checks with

Dallas Semiconductor Touch Memory Products.”

The shift register bits are initialized to 0. Then starting with the least significant bit of the family code,

1 bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number is

entered. After the 48

bit of the serial number has been entered, the shift register contains the CRC

value. Shifting in the 8 bits of CRC should return the shift register to all 0s.

64-BIT LASERED ROM Figure 4

8-BIT CRC CODE 48-BIT SERIAL NUMBER

8-BIT FAMILY CODE

(28h)

MSB LSB MSB LSB MSB LSB

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