单片机与PC机串口通信的设计(8)

At present the domestic use many is the MCS-51 series monolithic integrated circuit, therefore selects the monolithic integrated circuit experiment object is piece of AT89C51, Figure 1 is the hardware schematic diagram, because must realize conforms to the RS232C serial communication, but also should use one piece ICL232CPE(MAX232) to take the serial communication the level switching circuit. In

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experimental process, in order to examine corresponds whether succeeds, besides lets the monolithic integrated circuit return to on position machine delivers the data, but also expanded several piece of latches in the monolithic integrated circuit periphery, several LED light emitter diode and several small keyboards. The serial communication uses the simple TxD, RxD, GND three-wire system connection, pays attention to TxD and RxD nearby two should the overlapping segment.

On the position machine is ordinary PC machine, altogether has 2 serial port COM1, COM2, it moves RedHat8.0, in fact, if does not request to move graphical interfaces and so on Gnome or KDE, Linux is quite low to the system hardware request.

The experiment proved that, this electric circuit simple reliable, is suitable extremely for the test serial communication.

2 serial communication programming

Serial communication procedure including lower position machine monolithic integrated circuit and on position machine PC machine procedure. The monolithic integrated circuit receives the data which the position machine transmits, puts to internal RAM inside, again the data simultaneously transmits RAM in to exterior expansion latch and on the position machine, from this may judge corresponds whether succeeds. This procedure wrote by the assembly language, when initialization the baudrate establishment is 4 800 b/s, the mailing address is 8-N-1.

On the position machine procedure compilation is the essential part, because must carry on the operation to the serial port hardware equipment, some 2 methods, one are use Linux essence bringing the serial port driver, moreover one method is the direct read-write serial port hardware port, below introduced separately. 2.1 use serial port driver programming method

Carries on the programming using the Linux own serial port driver, in fact is transfers the driver a series of functions, completes the serial port correspondence parameter the establishment, the data transmission and the receive. In this method, Linux all assigns a document index number for each serial port, has the corresponding document name, in fact is regards as the hardware equipment one kind of special document, like COM1, COM2 correspondence document respectively be/dev/ttyS0,/dev/ttyS1, operates these 2 serial ports in fact operates these 2 documents, but with does not certainly have to the hardware equipment document operation to the ordinary document operation what differently, all may use same document I/The O transfer function (open, write, read, close), the similarity lies in with system call open() opens the serial port obtains after the corresponding equipment document description symbol, first must to it carry on the initialization, establishes some specific parameters, like baudrate, The data position, the input output way and so on, these parameters deposit in structtermios, function tcsetattr() may establish the serial port structtermios, tcgetattr() to be possible to obtain serial port struct termios. After established the correspondence parameter carries on read-write on available read and write to the serial port document. When operating procedure must pay attention to the user whether has to the serial port document which

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