DS18B20数字温度计：单线通信与多功能应用

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"单片机资料包，包含DS18B20数字温度计的特性、引脚分配和应用领域" 这篇资料包主要关注的是DS18B20这款单片机，它是一款专用于温度测量的数字温度计。其核心特点包括： 1. 独特的1-Wire接口：只需一个端口引脚即可实现通信，极大地简化了硬件设计，降低了系统复杂度。 2. 多滴落能力：支持分布式温度传感应用，意味着可以在同一总线上连接多个DS18B20传感器，形成温度监测网络。 3. 无需外部组件：DS18B20内部集成了所有必要的电路，用户无需额外添加元件，方便使用。 4. 电源管理：可通过数据线供电，工作电压范围为3.0V至5.5V。同时，它在待机时几乎不消耗电力。 5. 宽温工作范围：可测量的温度范围从-55°C到+125°C，相当于-67°F到+257°F，满足广泛的环境温度需求。 6. 高精度：在-10°C至+85°C范围内，精度可达±0.5°C，确保了温度测量的准确性。 7. 可编程分辨率：温度分辨率可配置为9到12位，提供灵活的数据输出选择。 8. 快速转换：能够在750毫秒内完成12位温度值的数字化转换，响应速度快。 9. 温度报警设置：用户可定义非易失性温度报警阈值，当温度超出预设范围时，设备会通过报警搜索命令标识并处理。 10. 应用广泛：DS18B20适用于恒温控制系统、工业系统、消费电子产品、普通温度计以及任何对温度敏感的系统，具有很高的实用价值。在引脚分配方面，DS18B20有三个关键引脚： - GND：接地，确保设备正常工作。 - DQ：数据输入/输出，执行1-Wire通信协议。 - VDD：电源输入，为传感器提供工作电压。总结来说，DS18B20是一款高效、精确且易于集成的数字温度计，适合多种环境下的温度监控需求。这个资料包对于了解和使用DS18B20单片机进行温度测量项目非常有价值。

DS18B20

5 of 26

OPERATION - MEASURING TEMPERATURE

The 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 default state. This

equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C. Following the issuance of

the Convert T [44h] command, a temperature conversion is performed and the thermal data is stored in

the scratchpad memory in a 16-bit, sign-extended two’s complement format. The temperature

information 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. The

MSB of the temperature register contains the “sign” (S) bit, denoting whether the temperature is positive

or negative.

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/Data Relationships Table 2

-1

-2

-3

-4

LSB

MSb

(unit = °C)

LSb

SSSSS2

MSB

TEMPERATURE DIGITAL OUTPUT

(Binary)

DIGITAL

OUTPUT

(Hex)

+125°C 0000 0111 1101 0000 07D0h

+85°C 0000 0101 0101 0000 0550h*

+25.0625°C 0000 0001 1001 0001 0191h

+10.125°C 0000 0000 1010 0010 00A2h

+0.5°C 0000 0000 0000 1000 0008h

0°C 0000 0000 0000 0000 0000h

-0.5°C 1111 1111 1111 1000 FFF8h

-10.125°C 1111 1111 0101 1110 FF5Eh

-25.0625°C 1111 1110 0110 1111 FF6Fh

-55°C 1111 1100 1001 0000 FC90h

*The power on reset register value is +85°C.

OPERATION - ALARM SIGNALING

After the DS18B20 has performed a temperature conversion, the temperature value is compared to the

trigger values stored in TH and TL. Since these registers are 8-bit only, bits 9-12 are ignored for

comparison. The most significant bit of TH or TL directly corresponds to the sign bit of the 16-bit

temperature register. If the result of a temperature measurement is higher than TH or lower than TL, an

alarm flag inside the device is set. This flag is updated with every temperature measurement. As long as

the alarm flag is set, the DS18B20 will respond to the alarm search command. This allows many

DS18B20s to be connected in parallel doing simultaneous temperature measurements. If somewhere the

temperature exceeds the limits, the alarming device(s) can be identified and read immediately without

having to read non-alarming devices.

DS18B20

6 of 26

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 eighth 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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DS18B20数字温度计：单线通信与多功能应用

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