Thread: C++ WriteFile() why dont I read the correct letter on the Hyperterminal?

  1. #1
    Registered User
    Join Date
    Jan 2003

    Question C++ WriteFile() why dont I read the correct letter on the Hyperterminal?

    Im using this code to address my ComPort:

    #pragma hdrstop
    #include <condefs.h>
    #pragma argsused
    #include <iostream.h>
    #include <stdio.h>
    #include <windows.h>
    int main()
     HANDLE HdComm;
     DWORD DwError;
     DCB Dcb;
     unsigned char Msg[128], Data;
     //int RealNum;
     DWORD RealNum;
     // Open the COMM port.
     HdComm = CreateFile( "COM1", GENERIC_READ | GENERIC_WRITE, 0,
     if ( HdComm == INVALID_HANDLE_VALUE /*cmaryus*/ ) // If COMM port can't be opened, then ...
        DwError = GetLastError();  // Display error code, and abort.
        FormatMessage( FORMAT_MESSAGE_FROM_SYSTEM, 0, DwError, 0, (char *)Msg, 124, 0 );
        printf( "Cannot Open Port COM1 !\nError Code: %d, - %s.\n", DwError, Msg );
        return 1;
     // Initialize COMM port.
     SetupComm( HdComm, 1024, 1024 );
     GetCommState( HdComm, &Dcb );
     Dcb.BaudRate = BAUD_9600;
     Dcb.Parity = NOPARITY;
     Dcb.ByteSize = 8;
     Dcb.StopBits = ONESTOPBIT;
     SetCommState( HdComm, &Dcb );
     do {
    //    ReadFile( HdComm, &Data, 1, &RealNum, NULL );    //Recieve the char from COM1
        WriteFile( HdComm, &Data, 1, &RealNum, NULL );    //Write the recieved data to COM1
        printf( "%02x    ", Data );                       //Display the data
     } while( Data != 0x1b );                             // Loop until the data is ESC
     CloseHandle( HdComm );
     return 0;
    When I check the Com1Port with the other PC`s Hyperterminal I don`t get the a, I get squares.

    Im trying to send to a 8051 P , and would like to know what the ComPort sbuf really puts out.
    What do I have to send for Data and what does the Sbuf turn out?



  2. #2
    train spotter
    Join Date
    Aug 2001
    near a computer
    >>I get squares

    sounds like string terminators. Is the data there to be read?

    Try testing the amount read (by looking at the values in dwBytesRead (RealNum) and the return.

    both == 0 is error in read

    (dwBytesRead==0)&&(iReturn!=0) == EOF or no data
    "Man alone suffers so excruciatingly in the world that he was compelled to invent laughter."
    Friedrich Nietzsche

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    George Best

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    Winston Churchill

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