【正文】 on requirements are 1μF/25V1 should choose its value and should be as close as possible tantalum chip capacitor 1C5 is 0. 1μF decoupling capacitor. MAX232 pin T1IN, T2IN, R1OUT, R2OUT to pick TTL / CMOS level pin 1 pin T1OUT, T2OUT, R1IN, R2IN to access RS 232C level 1 so the pin TTL / CMOS level T1IN, T2IN MCS51 pin should be connected to the serial transmit pin TXD。 if not, it quits the interrupt. D. The processing subprogram of send interrupts The processing subprogram of send interrupts is responsible to send data to the puter, sending interrupt state is off in the general. When the munication program pletely deals with data sent by PC microputer, the symbol “1” can be written to send buffer. As the puter receives the symbol “1”, it is said that single chip puter executes pletely the introduction sent by PC microputer. Therefore the serial port interrupt is set as “off” state by the single chip microcontroller and it is set “on” state again after the data are sent. So the single chip microputer returns to main program and waits for receiving instructions. V. THE DESIGN OF COMMUNICATION PROGRAM OF PC MICROCOMPUTER AND SINGLE CHIP MICROCOMPUTER In order to realize the system software easily grafted and uniformity, the program of upper puter is designed using the Boland C++ Builder as a programming tool in the control system s the Boland C++ Builder as a programming tool for PC programming. The serial port munication can be utilized in two ways: First, register ponents, C++ Builder does not in itself provide a separate serial munication ponent, but it can be obtained through registered Microsoft MSComm32 ponents, in which it is relatively simple for VB, VC in this way. The second method is called Windows API (Application Program Interface) function, in which this function is provided by the operating system in order to provide a lot of executive function. The program steps are followed: (1) Setting by munication protocol and opening the serial port, which is called initialization, then blocking the other programs to use the serial port. (2) Configuring the serial port. (3) Transmitting data by the serial port to and fro, verifying data during transmission. (4) Closing the serial port as no needing it so that other program uses. The subinterface is simple, in which the setting on subinterface parameters are defaults, such as baud rate that single chip munication module has been set to 2400Bps and that the baud rate is set to 2400Bps in the puter settings on the ports. The PC microputer has two ports called as serial port COM1 and COM2 generally, so the program can automatically identify serial port so that it can send and receive data and instructions successfully. Serial munication program includes two aspects, one is MCS51 microcontroller munication program, on the other hand for the PC, the munication process. In the 9 preparation processes, the development of the two protocols is very important, otherwise it will not guarantee the reliability of data munications, and thus lose the meaning of munication. The munication protocol is agreed as follows: 1) The serial munication baud rate is 1200bps. 2) The frame format is: a start bit, eight data bits, a programmable ninth bit (this bit is sent and received address / data flag), and one stop bit. 3) Set the address of the microcontroller code F1H. Contact before sending the data in the address code, such as the address code is the correct transmission of data, or to contact the address code. 4) no parity. The munication of data accumulation and verification of the method, that is, each carrying one set of data (number of custom, is set to 100), a cumulative and whether the correct checksum, the right to send you back to the 00H, or loopback FFH. 5) munication can interrupt transmission and query. Here are ways to search for in the munication. 6) PCcontact for the initiative to contact MCS 51 microcontroller. 7) PC machine using COM2 munications. VI. CONCLUSION The hardware of serial port munication is designed based on RS232, and the software of munication module between PC microputer and single chip microputer were programmed by using C++ Build and assembly langua ge. The control system runs well on industry field, and controls the stepping motor? Start/Stop and Forward/Reversal rotation by controlling single microputer. The PC microputer sends out control instruction to the single microputer by friendly user interface. 10 REFERENCES [1] Fan Yizhi, Jiang Wenxiang, Chen Liyuan. Serial munication control based C++Build and RS232. Beijng: Tsinguua University Press, 2020, pp. 218 [2] Gou Suai. C++Builder Programmer?s Guide. Beijing: Beijing Hope Electronic Press, 2020, pp. 16 [3] Liu Yanling. The Use of Communication Between MCS51 Single Chip Microputer and PC Microputer with MAX232. Journal of Tianjin Institute of Technology, 1999, Vol, 15(2): pp. 5658 [4] Yang Guoxia. Dealing With The Data Communication Between The Serial Port And The Main Progra