#define BUFSIZE 200
    HANDLE Comm;
    char Data[BUFSIZE];
    Comm = CreateFile(
        "COM1",                        // pointer to name of the file
        GENERIC_READ|GENERIC_WRITE,    // access (read-write) mode
        0,                            // share mode
        0,                            // pointer to security attributes
        OPEN_EXISTING,                // how to create
        FILE_ATTRIBUTE_NORMAL,        // file attributes
        0                             // handle to file with attributes to copy
                      );
    BuildCommDCB(
        "baud=115200 parity=N data=8 stop=1",  // pointer to device-control string
        &CommDCB     // pointer to device-control block
                );

    CommDCB.fOutX = true;
    CommDCB.fOutxDsrFlow = false;
    CommDCB.fDtrControl = DTR_CONTROL_DISABLE;
    CommDCB.fDsrSensitivity = false;
    CommDCB.fRtsControl = RTS_CONTROL_DISABLE;
    CommDCB.StopBits = ONESTOPBIT;
    CommDCB.XonChar = 'Q'-0x40;
    CommDCB.XoffChar = 'S'-0x40;
    CommDCB.EofChar = -1;
    CommTO.ReadIntervalTimeout = 0;
    CommTO.ReadTotalTimeoutMultiplier = 0;
    CommTO.ReadTotalTimeoutConstant = 100;
    CommTO.WriteTotalTimeoutMultiplier = 0;
    CommTO.WriteTotalTimeoutConstant = 0;

    i = SetCommTimeouts(
        Comm,    // handle to communications device
        &CommTO    // address of communications time-out structure
                       );
    i = SetCommState(
        Comm,    // handle to communications device
        &CommDCB    // address of device-control block structure
                    );

    DWORD i;
    ReadFile(Comm, Data, BUFSIZE, &i, 0);
    if(i!=0)
    {
        пришло i байтов данных, обрабатываем
    }