DS18B20数字温度传感器技术详解

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"DS18B20 是一种数字温度传感器，常用于各种分布式温度检测应用。这款传感器具有独特的1-Wire接口，只需要一个端口引脚就能进行通信，简化了多点温度测量的设计。此外，它不需要额外的外部组件，可以从数据线上获取电源，供电范围在3.0V到5.5V之间，并且在待机时功耗为零。" DS18B20的主要特性包括： 1. **1-Wire接口**：这种接口允许通过单根信号线（数据线DQ）实现与微控制器的通信，大大减少了硬件需求。 2. **多滴能力**：传感器可以串联在同一条总线上，形成一个多点温度测量系统，便于构建分布式温度监测网络。 3. **无外部组件**：DS18B20内置电源管理，无需外部元件即可工作。 4. **电源电压范围**：3.0V至5.5V，适应性广，适用于多种电源环境。 5. **零待机功率**：在不工作时，传感器几乎不消耗能量，有利于节能设计。 6. **温度范围**：可测量-55°C到+125°C的温度，相当于-67°F到+257°F，覆盖了大多数应用的温度区间。 7. **精度**：在-10°C到+85°C的范围内，精度可达±0.5°C，确保了高精度的温度测量。 8. **可编程分辨率**：用户可以根据需要设置温度分辨率，范围在9到12位之间，以满足不同精度需求。 9. **快速转换时间**：12位温度数据转换至数字值的时间最快只需750毫秒，提高了实时性能。 10. **温度报警功能**：用户可以设置非易失性温度报警阈值，当温度超出预设范围时，可通过报警搜索命令识别并处理。 11. **广泛应用**：DS18B20适用于恒温器控制、工业系统、消费产品、温度计以及任何对温度敏感的系统。 **引脚分配**： - GND（接地）：连接系统的地线。 - DQ（数据输入/输出）：这是1-Wire通信的唯一数据线，既用于发送也用于接收数据。 - VDD（电源电压）：连接到3.0V至5.5V的电源。 - NC（无连接）：不连接到任何电路，可能用于未来扩展或预留。 DS18B20是一款集成度高、使用方便、精度可靠的数字温度传感器，适用于多种温度监测场景，通过其1-Wire特性，可以在有限的硬件资源下实现复杂的温度监控系统。

DS18B20

6 of 27

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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