【正文】 mostly level TTL or CMOS, so the munication, the need for level conversion, so with the RS 232C standard level matching 1MAX232 chip level conversion can be done in this work. 4 RS232 is defined as the singleended standards, which has much characteristic, such as more munication distance in a lowspeed serial munications, moderate price and good practicality of the system, so it is most appropriate to be a munication port. RS232 is an essential modern puter interface, it includes ports COM1 and COM2, the port COM1 has 9pin connector. The new generation puter has a 9pin connector (DB9) so as to connect with the RS232 munication port. In order to achieve reliable and real time transmission, the system adopt a threewire connection method, that is to say that the GND pin, RXD pin and TXD pin of RS232 port is connected with the external port, it is shown in Figure 1. Figure 1. The RS232 port III. THE HARDWARE DESIGN OF SERIAL PORT COMMUNICATION The inout level of single chip puter is TTL level, while the RS232 serial interface of a PC puter is standard serial interface, so both the electrical specifications are inconsistent. In order to municate with the upper and lower puter, it is needed that the out level of single chip puter is changed to the TTL level. The mon level converter chip between TTL and RS232 level is MCI1488 and MCI1489. The MCI1488 converts TTL level to RS232 level, it needs the supply voltage of 177。 12V, and that the MCI1489 converts the RS232 standard level TTL level, it needs power supply voltage of +5V. Due to three power supply voltage, the circuit will be plicated, so this circuit adopts the standard RS232 chip MAX232. MAX232 is the product of the MAXIM Company。因此，PC 微機和驅(qū)動系統(tǒng)之間的通信是系統(tǒng)通信所必需的。串行通信是一個數(shù)據(jù)按一個個序位單向傳輸?shù)耐ǖ溃渲袃蓚€過渡線是實現(xiàn)雙向通信傳輸?shù)男枰? 盡管相對較慢的傳輸速度遠低于并行端口，串行端口通信依然因為它簡單的設(shè)備和高的成本效益而成為一個受歡迎的連接選項。其他可以在任何時間發(fā)送或接收被稱為單雙工設(shè)備。大多數(shù)串行設(shè)備傳輸七、八位數(shù)據(jù)。同步通信適用于傳送速度高的情況 ,其硬件復(fù)雜。 智能傳感器的 CMOS 芯片因為其低成本，小型化，智能化和標(biāo)準(zhǔn)化的特點已得到廣泛應(yīng)用。許多短距離打印機等電腦外設(shè)，所有磁盤和終端與 PC 機通過 RS232串行接口通信。 RS232是一個基本現(xiàn)代化的計算機接口，它包括 COM1和 COM2端口，該端口 COM1有九針連接器。由于適用三個電源電壓，電路將不可避免地變得復(fù)雜，所以該電 路采用標(biāo)準(zhǔn)的 RS232芯片MAX232。因此 TTL/CMOS 電平的 T1IN、 T2IN 引腳應(yīng)接 MCS51的串行發(fā)送引腳 TXD； R1OUT、 R2OUT 應(yīng)接 MCS51的串行接收引腳 RXD，與之對應(yīng)的 RS232C 電平的 T1OUT、 T2OUT 應(yīng)接 PC 機的接收端 RD； R1IN、 R2IN 應(yīng)接 PC機的發(fā)送端 TD。中斷服務(wù)子程序流程圖如圖 3所示。同時，單片機重新載入由 PC 機通過串行通信微機發(fā)送的初始值。隨著計算機接收代碼“ 1”，這表明，單片機上執(zhí)行完全由 PC 微機發(fā) 送的指令。 （ 3）傳遞串口轉(zhuǎn)來的數(shù)據(jù)，驗證數(shù)據(jù)的傳輸過程。 （ 3）設(shè)定單片機的地址碼為 F1H。 六、結(jié)論 串口通信的硬件設(shè)計基于 RS232， PC機和單片機之間進行通信的軟件模塊使用 C++和匯編語言編程。 （ 6）聯(lián)絡(luò)方式為 PC 機主動聯(lián)絡(luò) MCS51單片機?，F(xiàn)約定其通信協(xié)議如下 : （ 1）串行通信波特率為 1200bps。該設(shè)計的步驟如下： （ 1）設(shè)置通信協(xié)議，打開串行端口，這是所謂的初始化，然后阻止其他程序使用串行端口。 D 發(fā)送中斷處理子程序 發(fā)送中斷處理子程序負責(zé)將數(shù)據(jù)發(fā)送到計算機，中斷狀態(tài)一般為不允許中斷。 15 B 發(fā)送步 進脈沖子程序 使用反單晶片微控制器定時器 0，作為固定的時間計時，能使 ，從而產(chǎn)生周期性的驅(qū)動脈沖。 圖 2 串行通信模塊的硬件電路 四、串口通信的軟件設(shè)計 單片機的通信程序與 PC 機之間通過中斷通信， PC 機被稱為主控制器。其取值均為 1μ F/25V，宜選用鉭電容并且應(yīng)盡量靠近芯片， C5為 F 的去耦電容。 TTL 電平可由 MCI1488轉(zhuǎn)換為 RS232電平，它需要177。 MAX232芯片可以完成電平轉(zhuǎn)換這一工作。 RS232是在 PC 機中和通信行業(yè)中應(yīng)用最廣泛的的串行接口。在 PC 機中一般有兩個標(biāo)準(zhǔn) RS232C 串行接口 COM1和 COM2。大多數(shù)系列設(shè)備使用 9針連接器。波特率是數(shù)據(jù)從一個設(shè)備到另一個的傳輸速度。 12 如前所述，一個串行設(shè)備一次發(fā)送和接收一個位的數(shù)據(jù)。 要使串行通信工作，你只需要一根三根線的電纜 —— 1根發(fā)送， 1根用來接收， 1根接地。但是當(dāng)傳輸距離遠，并且傳輸數(shù)據(jù)的數(shù)量很多時，它需要的傳輸線的數(shù)目也更多。實現(xiàn)了分別在 PC 微機和單片機中使用匯編語言和 C++Builder 的編程。 program design. I. INTRODUCTION During working in the control system, the PC microputer sends instructions for stepbystep motor to collect the image information. Therefore the munication between the PC microputer and the driving system is needed for the munication system. In general, a plete munication system consists of transmitter, receiver, converting the data interface and transmitting data channel. The control of the stepbystep motor is realized through the pulse distribution by single chip microputer. On the motor control system, the PC microputer is called as upper puter, and the single chip microputer for driving stepbystep motor is called as lower puter. The munication between the upper puter and the lower puter has two methods, that is to say the parallel munication and serial munication. Parallel interface can transmit much data at the same time and has the fast speed, but when the transmission distance is far and the number of data is much, it needs more the number of transmission lines. In addition, the voltage level may be changed by the transmission line factor and electromagic interference. Serial munication is a one way that the data is transmitted by a bit in order, in which two transition lines is needed to realize bidirectional munication. It is taken into consideration that the data is much and the transmutation number is little, the serial munication is utilized in the control system so as to simplify the hardware and save the cost. Serial munication is one of the oldest mechanisms for devices to municate with each other. Starting with the IBM PC and patible puters, almost all puters are equipped with one or more serial ports and one parallel port. As the name implies, a serial 2 port sends and receives data serially, one bit at a time. In contrast, a parallel port