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

Hi,
Im using this code to address my ComPort:

Code:

#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;
    Data='a';
 // Open the COMM port.
 HdComm = CreateFile( "COM1", GENERIC_READ | GENERIC_WRITE, 0,
  NULL, OPEN_EXISTING, 0, NULL );
 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 );
    //cout<<Data;
 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.

I´m trying to send to a 8051 µP , 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?

Thanks

Johannes