文档介绍：摘要
现场总线是目前国际上过程控制领域的一个热点,通过现场总线数字通信技术可以延伸到现场级仪表,给控制体系带来一场革命。考虑到我国目前传统的基于4~20mA的模拟设备仍然广泛的应用于工业控制,为满足从模拟到全数字的过渡HART协议应运而生。该协议基于Bell202通信标准,在4~20mA的模拟信号上叠加不同的频率信号来传送数字信号。其特点是在现有的模拟信号传输线上实现数字信号通信,属于模拟系统向数字系统转变过程中的过渡产品,由于这项技术属于承前启后的研究,所以,在当前的过渡时期具有较强的市场竞争能力,得到了较快发展。
本文主要讨论HART协议通信模块的硬件相关方面的设计。首先,论文对HART协议做了较全面的分析。HART协议采用ISO/OSI简化模型,ISO/OSI分为七个功能层,HART协议只用了第一、二、七层即物理层、数据链路层和应用层。其中物理层规定了信号的传输方式以及信号电平等内容,数据链路层规定了设备类型以及数据传输帧格式,应用层规定了HART协议的各种命令及响应码。其次,论文以HART协议为通信标准,提出了通信板的硬件设计的总体方法。论文在介绍了HART协议的基础上着重研究了硬件设计,硬件上较为详尽的介绍了各个组成模块——微处理器模块、电流环模块、调制解调器模块的功能和实现方法。
关键词:现场总线;HART协议;通信模块;ADuC812单片机
Abstract
Nowadays,fieldbus technique became very important in the world of process control,through which munication is used to fields instruments,this leads to a revolution to control ,4~20mA analog signal instruments alse have a large application in industry,the munication protocol—a transitional protocol during transition from analog system to digital system—emerges as the times on munication standards,HART protocol transfer data with different frequency signals and plus with analog signals of 4~ is characteristic that realizes munication in the transmission of analog signals,it has petition in this interim period and grows quickly because of this technology belongs to research of link between the preceding and the following.
In this paper, it mainly focuses on HART munication module hardware-related aspects of the design. Firstly, the thesis does a prehensive analysis of the HART protocol. it adopt a predigested mode of OSI/ISO in which have seven functional layers,only three layers havebeen used in HART Layer specifies the transmittal manner of signal and voltage of signal,Data Link Layer specifies the device type and format of data mand Layer specifies all kinds of mand and reoponse codes. At the basis of HART protocol ,it focused on studying hardware design.
Secondly,being based upon HART protocol,the Overall approach about