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### 18b20 数字温度传感器详细解析 #### 一、概述 18b20是一款由Dallas Semiconductor（达拉斯半导体）生产的数字温度传感器，具有独特的单总线（1-Wire）通信接口，这使得它只需要一条数据线即可完成与微处理器之间的通信。这种特性简化了分布式温度传感系统的布线复杂度，并且减少了所需的硬件资源。 #### 二、特点 1. **独特的单总线接口**：18b20通过单总线接口进行通信，这意味着仅需一个端口引脚就能实现数据交换。 2. **多路复用能力**：支持多个18b20设备连接到同一总线上，便于在大型系统中进行分布式温度监测。 3. **无需外部元件**：内部集成了所有必要的功能，不需要额外的外部组件。 4. **可从数据线供电**：可以在不使用外部电源的情况下从数据线获取电力，供电范围为3.0V至5.5V。 5. **零待机功耗**：在待机状态下几乎不消耗电力。 6. **测量范围广泛**：可以测量-55°C至+125°C（或-67°F至+257°F）的温度范围。 7. **高精度**：在-10°C至+85°C范围内，测量精度可达±0.5°C。 8. **可编程分辨率**：温度分辨率可以从9位到12位之间进行编程设置。 9. **快速转换时间**：能够在最大750毫秒内将12位的温度值转换为数字信号。 10. **用户定义的非易失性温度报警设置**：允许用户设定温度报警阈值，并且这些设置被保存在非易失性存储器中，即使断电也不会丢失。 11. **报警搜索命令**：能够识别并定位那些温度超出预设限制的设备，方便进行远程监控和管理。 #### 三、引脚说明 18b20拥有三个主要引脚： - **GND**：接地引脚。 - **DQ**：数据输入/输出引脚，用于单总线通信。该引脚采用开漏设计。 - **VDD**：电源电压引脚，用于提供3.0V至5.5V的电源电压。如果选择寄生电源模式，则此引脚可以悬空。 #### 四、应用领域 18b20数字温度传感器的应用十分广泛，包括但不限于以下几个方面： 1. **温控系统**：适用于各种家用电器和工业设备中的温度控制系统。 2. **工业系统**：如自动化生产线上的温度监测。 3. **消费产品**：如智能温湿度计等智能家居产品。 4. **温度计**：可用于便携式电子温度计的设计。 5. **热敏系统**：对温度敏感的各种系统，如精密仪器和实验室设备。 #### 五、技术细节 1. **分辨率可配置**：用户可以根据实际需求，在9位到12位之间设置温度分辨率。分辨率越高，温度测量的精度也越高，但相应的数据处理时间也会更长。 2. **单总线通信协议**：18b20采用了单总线通信协议，支持主从模式通信，可以通过简单的上拉电阻实现与微处理器的数据交换。 3. **唯一性标识码**：每个18b20芯片内部都嵌入了一个唯一的64位硅序列号，这使得在单总线上可以连接多个18b20设备，并通过这个序列号来区分不同的设备。 4. **寄生电源模式**：为了进一步减少外部硬件的需求，18b20支持寄生电源模式。在这种模式下，18b20可以直接从数据线上获取所需的电力，而不需要独立的电源引脚。 5. **报警功能**：18b20支持用户自定义的温度报警功能。用户可以设置温度上限和下限，当检测到的实际温度超出设定范围时，会触发报警。 18b20是一款非常实用的数字温度传感器，其独特的单总线通信接口、宽广的测量范围以及高精度等特点使其成为许多温度敏感应用的理想选择。无论是家用还是工业用途，18b20都能提供准确可靠的温度测量服务。

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1 of 27 050400

FEATURES

 Unique 1-Wire interface requires only one

port pin for communication

 Multidrop capability simplifies distributed

temperature sensing applications

 Requires no external components

 Can be powered from data line. Power supply

range is 3.0V to 5.5V

 Zero standby power required

 Measures temperatures from -55°C to

+125°C. Fahrenheit equivalent is -67°F to

+257°F

 ±0.5°C accuracy from -10°C to +85°C

 Thermometer resolution is programmable

from 9 to 12 bits

 Converts 12-bit temperature to digital word in

750 ms (max.)

 User-definable, nonvolatile temperature alarm

settings

 Alarm search command identifies and

addresses devices whose temperature is

outside of programmed limits (temperature

alarm condition)

 Applications include thermostatic controls,

industrial systems, consumer products,

thermometers, or any thermally sensitive

system

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

- Power Supply Voltage

NC - No Connect

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 central 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. This 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.

DS18B20

Programmable Resolution

1-Wire

Digital Thermomete

www.dalsemi.com

PRELIMINARY

DALLAS

DS1820

1 2 3

GND

VDD

1 2 3

BOTTOM VIEW

DS18B20 To-92

Package

GND

DS18B20Z

8-Pin SOIC (150 mil)

DS18B20

2 of 27

DETAILED PIN DESCRIPTION Table 1

8PIN SOIC

TO92 SYMBOL DESCRIPTION

5 1 GND Ground.

42DQData Input/Output pin. For 1-Wire operation: Open

drain. (See “Parasite Power” section.)

33V

Optional V

pin. See “Parasite Power” section for

details of connection. V

must be grounded for

operation in parasite power mode.

DS18B20Z (8-pin SOIC): All pins not specified in this table are not to be connected.

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

triggers 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 until it

returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may also be

powered from an external 3 volt - 5.5 volt supply.

Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control

functions will not be 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 specific 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 memory 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 DS18B20’s scratch-pad memory, and may be read by issuing a

memory function command which reads the contents of the scratchpad 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 temperature 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.

DS18B20

3 of 27

DS18B20 BLOCK DIAGRAM Figure 1

PARASITE POWER

The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power

whenever the DQ or V

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, 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. 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 pullup on the DQ line whenever temperature conversions or copies

to the E

memory are taking place. This may be accomplished by using a MOSFET to pull the DQ line

directly to the power supply as shown in Figure 2. The DQ line must be switched over to the strong pull-

up within 10 µs maximum after issuing any protocol that involves copying to the E

memory or initiates

temperature conversions. When using the parasite power mode, the V

pin must be tied to ground.

Another method of supplying current to the DS18B20 is through the use of an external power supply tied

to the V

pin, as shown in Figure 3. The advantage to this is that the strong pullup is not required on the

DQ line, and the bus master need not be tied up holding that line high during temperature conversions.

This allows other data traffic on the 1-Wire bus during the conversion time. In addition, any number of

DS18B20s may be placed on the 1-Wire bus, and if they all use external power, they may all

simultaneously perform temperature conversions by issuing the Skip ROM command and then issuing the

Convert T command. Note that as long as the external power supply is active, the GND pin may not be

floating.

The use of parasite power is not recommended above 100°C, since it may not be able to sustain

communications given the higher leakage currents the DS18B20 exhibits at these temperatures. For

applications in which such temperatures are likely, it is strongly recommended that V

be applied to the

DS18B20.

64-BIT ROM

AND

1-WIRE PORT

MEMORY AND

CONTROL LOGIC

SCRATCHPAD

8-BIT CRC

ENERAT

TEMPERATURE SENSOR

HIGH TEMPERATURE

TRIGGER, TH

LOW TEMPERATURE

TRIGGER, TL

CONFIGURATION

POWER

SUPPLY

SENSE

INTERNAL V

DS18B20

5 of 27

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.

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caoqi618

2011-10-31

怎么是英文版的呢，和标题不合呀

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