基于PIC16F74单片机串行通信中继控制器

字数:16274,页数:39   论文编号:JD342

中文摘要
目前，监控系统的应用无处不在，而在要监控范围大或监控点数多的情况下，就需要把监控工作分散进行，而把监控结果集中管理，这就是所谓的分布式监控。各种具有不同功能和接点数的模块可以随意组合成适合各种环境的分布式监控系统。连接这些分散的结点，最简单的方法就是采用串行总线结构[1]。
在多机通信领域，由于单片机具有灵活高效的多机通信功能和价格优势，应用越来越广泛，但由于单片机的收发信号都是TTL电平，驱动能力和抗干扰性有限，实用中常配合其它总线实现互联，RS485总线就是其中之一。RS485总线是平衡差分传输，抗干扰性好，最远可传输1200m，可互联多达31*31个单片机，非常适合组成多机通信系统。
RS485串行总线的单片机多机通信系统采用半双工主从通信方式，主机可以控制从机通信，从机主要负责对分布的电子设备进行监测或控制，从机接收主机发来的命令并做出相应的回答，同时从机间也可以通过总线进行通信。
在设计中，CPU采用了Microchip的8位处理器PIC16F74单片机。基于该单片机的高度集成化，可以简化外围电路，降低软件编写的难度，使系统具有更高的效率性，可靠性和经济性[2]。
本课题的难点和关键点就是软件的编写，最重要的是保证通信有条不紊地进行，因此需要严格和完善的通信协议。
该设计不但可以解决分布监控，采集数据集中管理难等的问题，而且可以解决远距离传输时常出现误码的问题，扩展通信距离。
本文全面介绍了基于PIC16F74的串行通信中继器的现状，PIC单片机的简单介绍，RS485通信、HT1621LCD显示、4*4键盘、外扩数据存储器和电源模块的硬件设计方案及其各模块的软件设计。

关键词：中继器，RS-485总线，PIC16F74单片机

The repeater of serial communications
based on PIC16F74 microcontroller
Abstract
At present,the monitoring system is ubiquitous. The work of monitoring is decentralized and the management of the monitoring results is centralized. This is so-called distributed control. To connect the scattered nodes, the simplest way is to use serial bus architecture.
In the field of multi-machine communication, MCU have a flexible and efficient multi-machine communication function, so its application is more and more extensive. But, because the SCM signal are TTL level, the limited capacity of driver and anti-jamming, in Practical application, used with other bus.RS485 bus is one of them. RS485 bus is the balance differential transmission, and have good anti-jamming. The farthest transmission distance is 1200 m. It can diver as many as 31 * 31 SCM, which very suitable for the multi-communication system.
RS485 Serial communication system is half-duplex, and the host MCU can control other MCU, which is mainly responsible for monitoring or controlling the decentralized electronic equipment,and receive orders from the host machine to make the appropriate answer.
In the design, CPU adopts the Microchip 8-bit processor PIC16F74.Because the MCU is highly integrated, the external circuit can be simplified .The price of pic16f74 is low.So the system is higher efficient, reliable and economical.
The difficulty of this issue or the key point is the software, which is to guarantee the orderly conduct of communications.So the strict and perfect communication protocol is the need.
The design not only can solve the distribution of monitoring, but also can solve transmission error problems in the long-distance, and can expand communication distance.
In this paper the actuality of the repeater of serial communications, brief of PIC MCU, RS485 communications, HT1621LCD, 4 * 4 keyboard, the expanded data storage and power modules and various modules Software design.

Key words: the repeater; RS-485 bus; PIC16F74

目录
中文摘要 I
Abstract II
第1章 绪论 1
1.1 几种总线的比较 1
1.1.1 RS-485 1
1.1.2 现场总线技术 1
1.1.3 本地互连网络LIN 1
1.1.4 USB总线 2
1.1.5 总线选择的标准 2
1.3 市场机遇 2
第2章 系统总体设计思想 3
2.1 系统总体设计思想 3
第3章 系统硬件设计 4
3.1 系统结构框图 4
3.2 系统主要模块介绍 4
3.2.1 单片机选择及外围电路设计 4
3.2.2 max485 总线 5
3.2.3 ht1621 LCD显示模块 6
3.2.4 4*4键盘 8
3.2.5 外扩数据存储器 9
3.2.6 电源设计 10
3.3 硬件抗干扰措施 11
第4章 系统软件设计 13
4.1 PIC单片机USART简介 13
4.2 通信协议 14
4.2.1 信息格式 14
4.2.2 定时与重发 15
4.2.3 程序流程图 15
4.2.4 几种通讯方案的对比 20
4.3 键盘软件设计 22
4.4 显示程序设计 26
4.5 数据存储器软件设计 26
4.6 软件抗干扰措施 28
4.8 MPLAB简介 28
第5章 系统存在的问题 30
结论 31
致谢 32
参考文献 33
附录1 PIC16F74单片机波特率计算 34