通信工程文献翻译——说明

DS18B20数字温度计提供 9-12位摄氏温度测量而且有一个由高低电平触发的可编程的不因电源消失而改变的报警功能。DS18B20 通过一个单线接口发送或接受信息，因此在中央处理器和DS18B20之间仅需一条连接线（加上地线）。它的测温范围为-55～＋125℃，并且在-10～＋85℃精度为±5℃。除此之外，DS18B20 能直接从单线通讯线上汲取能量，除去了对外部电源的需求。

每个DS18B20都有一个独特的64位序列号，从而允许多只DS18B20同时连在一根单线总线上；因此，很简单就可以用一个微控制器去控制很多覆盖在一大片区域的DS18B20。这一特性在HVAC环境控制、探测建筑物、仪器或机器的温度以及过程监测和控制等方面非常有用。

概览

图1是表示DS18B20的方框图，表1已经给出了引脚说明。64位只读存储器储存器件的唯一片序列号。高速暂存器含有两个字节的温度寄存器，这两个寄存器用来存储温度传感器输出的数据。除此之外，高速暂存器提供一个直接的温度报警值寄存器（TH 和 TL），和一个字节的的配置寄存器。配置寄存器允许用户将温度的精度设定为9，10，11 或 12 位。TH,TL 和配置寄存器是非易失性的可擦除程序寄存器（EEPROM），所以存储的数据在器件掉电时不会消失。

DS18B20通过达拉斯公司独有的单总线协议依靠一个单线端口通讯。当全部器件经由一个3态端口或者漏极开路端口（DQ引脚在DS18B20上的情况下)与总线连接的时候，控制线需要连接一个弱上拉电阻。在这个总线系统中，微控制器（主器件）依靠每个器件独有的64位片序列号辨认总线上的器件和记录总线上的器件地址。由于每个装置有一个独特的片序列码,总线可以连接的器件数目事实上是无限的。单总线协议，包括指令的详细解释和“时序”单总线系统。

DS18B20的另一个功能是可以在没有外部电源供电的情况下工作。当总线处于高电平状态，DQ与上拉电阻连接通过单总线对器件供电。同时处于高电平状态的总线信号对内部电容（Cpp）充电，在总线处于低电平状态时，该电容提供能量给器件。这种提供能量的形式被称为“寄生电源”。作为替代选择，DS18B20同样可以通过VDD引脚连接外部电源供电。

DS18B20方框图 图1

DESCRIPTION

The DS18B20 Digital Thermometer provides 9 to 12–bit centigrade 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 definition requires only one data line (and ground) for communication with a central microprocessor. It has an operating temperature range of –55°C to +125°C and is accurate to 0.5°C over the range of –10°C to +85°C. In addition, the DS18B20 can derive power directly from the data line (“parasite power”), eliminating 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 feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment or machinery, and process monitoring and control systems.

OVERVIEW

Figure 1 shows a block diagram of the DS18B20, and pin descriptions are given in Table 1. The 64-bit ROM stores the device’s unique serial code. The scratchpad 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 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 Dallas’ exclusive 1-wire bus protocol that implements bus communication 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 using each device’s unique 64-bit code. Because each device has a unique code, the number of devices that can be addressed on one bus.......