【正文】 nding the stepbystep impulse Using countertimer of the single chip microcontroller timer 0, as the fixed times plete, the port is negated so as to periodically generate the driving pulses. The timer 0 begins to count from initial value to 65535, then the interrupt subprogram of timer 0 is called, in which the port is negated to generate a driving pulse. Meanwhile, the single chip microputer loads again the initial value which is sent by the PC microputer by serial munication. 7 Figure 3. The flowchart of the interrupt service main subprogram C. The subprograms of judging instruction The program of judging instruction is set on the serial port interrupt program to be called. The PC microputer sends data to the single chip microputer. After the single chip microputer receives data, it sets the RI higher and called the serial port interrupt subprogram, in which the first data is processed. If the first data is a digital symble”48”, the serial port interrupt subprogram sets higher, then the next five bytes data is used to ensure the stepbystep motor? speed and steps. If the first data is a digital symble”49”, it means that the stepbystep motor reverses, then the single chip microputer receives the speed and steps information. Otherwise the single chip microputer judges that the 8 received data is not STOP instruction, if so, it sends “stop” instruction to the drive system。 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。 1 中文 4700 字 The Designing of Serial Communication Based on RS232 Abstract This paper discussed the principle of serial munication mainly, proposed the design method based on RS232, designed the hard circuit of serial munication, and realized the programming to PC Microputer and single chip microputer by using assembly language and C++ Builder separately. Keywords: serial munication。 its disadvantage is that transmission speed is low. As mentioned, a serial device sends and receives data one bit at a time. Some devices can send and receive data at the same time and are known as fullduplex devices. Others that can either send or receive at any one time are known as singleduplex. To initiate transmission, a device first transmits a start bit, followed by the data bits. The data bits can be five, six, seven, or eight bits, depending on what has been agreed upon. Both the sender and the receiver must be set to the same data bits for munication to take place correctly. Once the data bits are sent, a stop bit is sent. A stop bit can be one, one and a half, and two bits. The baud rate is the speed of transmission of data from one device to another. Baud rate is usually measured in bits per second (bps).Most serial devices transmit in seven or eight bits. To detect that the data has been sent correctly, an optional parity bit can be included together with the data bits. A parity bit can be one of the following: odd, even, mark, space, or none (mark and space parity are almost always used). Using a parity bit provides a basic mechanism to detect corruption of data that was sent and does not guarantee that the data received is free from error. Nevertheless, a parity bit is useful for improving the integrity of the data sent. Most serial ports adhere to the RS232C standard, which specifies a connector either with 25 pins or with 9 pins. Most serial devices use the ninepin connector. Serial munication with asynchronous munication and synchronous munication are two basic means of munication. Synchronous munication for the case of high transmission speed, the hardware plexity. The asynchronous munication 3 used in transmission speed between 50 and 19200 baud. Transmission is relatively mon. In asynchronous munication, data is transmitted frame by frame, each frame of serial data format by a start bit, 5 to 8 data bits, a parity bit (optional) and a Stop bit of four parts. Before the serial munication, the sender and receiver to agree the specific data format and baud rate (munication protocol). PCprogrammable serial asynchronous munication controller 8250 to implement asynchronous serial munication. By 8250 the initial programming, you can control serial data transmission format and speed. In the PC, in general there are two standard RS232C serial interface COM1 and COM21MCS 51 series microcontroller chip includes a fullduplex serial interface, can also be realized by programming the serial munications. CMOS smart sensor IC has received wide application for low cost, miniaturization, intelligence and standardization. In smart sensor IC designs, the munication interface circuits also play an important role other than sensors and signal processing circuits. There are more serial munication standard interfaces, such as RS232, RS485, USB Interface, IEEE1394, which has itsel