基于PIC16F74單片機(jī)串行通信中繼控制器

電子機(jī)電論文編號(hào):JD342 字?jǐn)?shù):16274,頁(yè)數(shù):39  

目錄
中文摘要 I
Abstract II
第1章 緒論 1
1.1 幾種總線的比較 1
1.1.1 RS-485 1
1.1.2 現(xiàn)場(chǎng)總線技術(shù) 1
1.1.3 本地互連網(wǎng)絡(luò)LIN 1
1.1.4 USB總線 2
1.1.5 總線選擇的標(biāo)準(zhǔn) 2
1.3 市場(chǎng)機(jī)遇 2
第2章 系統(tǒng)總體設(shè)計(jì)思想 3
2.1 系統(tǒng)總體設(shè)計(jì)思想 3
第3章 系統(tǒng)硬件設(shè)計(jì) 4
3.1 系統(tǒng)結(jié)構(gòu)框圖 4
3.2 系統(tǒng)主要模塊介紹 4
3.2.1 單片機(jī)選擇及外圍電路設(shè)計(jì) 4
3.2.2 max485 總線 5
3.2.3 ht1621 LCD顯示模塊 6
3.2.4 4*4鍵盤(pán) 8
3.2.5 外擴(kuò)數(shù)據(jù)存儲(chǔ)器 9
3.2.6 電源設(shè)計(jì) 10
3.3 硬件抗干擾措施 11
第4章 系統(tǒng)軟件設(shè)計(jì) 13
4.1 PIC單片機(jī)USART簡(jiǎn)介 13
4.2 通信協(xié)議 14
4.2.1 信息格式 14
4.2.2 定時(shí)與重發(fā) 15
4.2.3 程序流程圖 15
4.2.4 幾種通訊方案的對(duì)比 20
4.3 鍵盤(pán)軟件設(shè)計(jì) 22
4.4 顯示程序設(shè)計(jì) 26
4.5 數(shù)據(jù)存儲(chǔ)器軟件設(shè)計(jì) 26
4.6 軟件抗干擾措施 28
4.8 MPLAB簡(jiǎn)介 28
第5章 系統(tǒng)存在的問(wèn)題 30
結(jié)論 31
致謝 32
參考文獻(xiàn) 33
附錄1 PIC16F74單片機(jī)波特率計(jì)算 34

中文摘要
目前，監(jiān)控系統(tǒng)的應(yīng)用無(wú)處不在，而在要監(jiān)控范圍大或監(jiān)控點(diǎn)數(shù)多的情況下，就需要把監(jiān)控工作分散進(jìn)行，而把監(jiān)控結(jié)果集中管理，這就是所謂的分布式監(jiān)控。各種具有不同功能和接點(diǎn)數(shù)的模塊可以隨意組合成適合各種環(huán)境的分布式監(jiān)控系統(tǒng)。連接這些分散的結(jié)點(diǎn)，最簡(jiǎn)單的方法就是采用串行總線結(jié)構(gòu)[1]。
在多機(jī)通信領(lǐng)域，由于單片機(jī)具有靈活高效的多機(jī)通信功能和價(jià)格優(yōu)勢(shì)，應(yīng)用越來(lái)越廣泛，但由于單片機(jī)的收發(fā)信號(hào)都是TTL電平，驅(qū)動(dòng)能力和抗干擾性有限，實(shí)用中常配合其它總線實(shí)現(xiàn)互聯(lián)，RS485總線就是其中之一。RS485總線是平衡差分傳輸，抗干擾性好，最遠(yuǎn)可傳輸1200m，可互聯(lián)多達(dá)31*31個(gè)單片機(jī)，非常適合組成多機(jī)通信系統(tǒng)。
RS485串行總線的單片機(jī)多機(jī)通信系統(tǒng)采用半雙工主從通信方式，主機(jī)可以控制從機(jī)通信，從機(jī)主要負(fù)責(zé)對(duì)分布的電子設(shè)備進(jìn)行監(jiān)測(cè)或控制，從機(jī)接收主機(jī)發(fā)來(lái)的命令并做出相應(yīng)的回答，同時(shí)從機(jī)間也可以通過(guò)總線進(jìn)行通信。
在設(shè)計(jì)中，CPU采用了Microchip的8位處理器PIC16F74單片機(jī)�；�于該單片機(jī)的高度集成化，可以簡(jiǎn)化外圍電路，降低軟件編寫(xiě)的難度，使系統(tǒng)具有更高的效率性，可靠性和經(jīng)濟(jì)性[2]。
本課題的難點(diǎn)和關(guān)鍵點(diǎn)就是軟件的編寫(xiě)，最重要的是保證通信有條不紊地進(jìn)行，因此需要嚴(yán)格和完善的通信協(xié)議。
該設(shè)計(jì)不但可以解決分布監(jiān)控，采集數(shù)據(jù)集中管理難等的問(wèn)題，而且可以解決遠(yuǎn)距離傳輸時(shí)常出現(xiàn)誤碼的問(wèn)題，擴(kuò)展通信距離。
本文全面介紹了基于PIC16F74的串行通信中繼器的現(xiàn)狀，PIC單片機(jī)的簡(jiǎn)單介紹，RS485通信、HT1621LCD顯示、4*4鍵盤(pán)、外擴(kuò)數(shù)據(jù)存儲(chǔ)器和電源模塊的硬件設(shè)計(jì)方案及其各模塊的軟件設(shè)計(jì)。

關(guān)鍵詞：中繼器，RS-485總線，PIC16F74單片機(jī)

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