Opening And Setting Up The Serial Port

It's not very hard to open and work with a serial port. The following example shows how to open the serial port as a file and set its parameters using the DCB.

Note: The variables SerialPort, BaudRate, Parity, BitsPerByte, StopBits, HardwareHandshaking, PortDesignator and WriteMode are presented with this code, but would normally be part of a header file or class definition.

typedef enum{COM1,COM2} PortDesignatorType;

typedef enum{None,Even,Odd,Mark} ParityType;

typedef enum{OneBit} StopBitsType;

typedef enum{Threaded,EchoHandshake,Dialog} WriteModeType;

         

PortDesignatorType        PortDesignator = COM1;

int                       BaudRate = 19200;

int                       ByteSize = 8;

ParityType                Parity = None;

StopBitsType              StopBits = OneBit;

int                       TimeOutInSeconds = 0;

bool                      HardwareHandshaking = true;

WriteModeType             WriteMode = Threaded;

         

AnsiString CommPort = (PortDesignator == COM1 ? "COM1" : "COM2");

         

HANDLE SerialPort =

             CreateFile

             (

               CommPort.c_str(),

               GENERIC_READ | GENERIC_WRITE,

               0, /* comm devices must be opened w/exclusive-access */

               NULL, /* no security attrs */

               OPEN_EXISTING, /* comm devices must use OPEN_EXISTING */

               WriteMode == Threaded ? FILE_FLAG_OVERLAPPED : FILE_ATTRIBUTE_NORMAL, /* Ansynchronous or Synchronous I/O   */

               NULL /* hTemplate must be NULL for comm devices */

             );

         

if (SerialPort == INVALID_HANDLE_VALUE)

{

             Application->MessageBox("Unable to open serial port","Error",0);

             return;

};

         

DCB    DeviceParameter;

         

GetCommState((void *) SerialPort,&DeviceParameter);

         

DeviceParameter.BaudRate = BaudRate;

DeviceParameter.ByteSize = ByteSize;

         

switch (Parity)

{

             case None: DeviceParameter.Parity = NOPARITY; break;

             case Even: DeviceParameter.Parity = EVENPARITY; break;

             case Odd: DeviceParameter.Parity = ODDPARITY; break;

             case Mark: DeviceParameter.Parity = MARKPARITY; break;

};

         

switch (StopBits)

{

             case OneBit: DeviceParameter.StopBits = ONESTOPBIT; break;

};

         

DeviceParameter.fParity = (Parity != NOPARITY);

DeviceParameter.fBinary = TRUE;

         

if (HardwareHandshaking)

{

}

else

{

             DeviceParameter.fOutxCtsFlow = FALSE; // CTS output flow control

             DeviceParameter.fOutxDsrFlow = FALSE; // DSR output flow control

             DeviceParameter.fDtrControl = DTR_CONTROL_DISABLE; // DTR flow control type

             DeviceParameter.fDsrSensitivity = FALSE;

             DeviceParameter.fRtsControl = RTS_CONTROL_DISABLE; // RTS flow control

             DeviceParameter.fInX = TRUE;

             DeviceParameter.fOutX = TRUE;

             DeviceParameter.fTXContinueOnXoff = FALSE;

             DeviceParameter.fNull = FALSE;

             DeviceParameter.XonLim = 10;

             DeviceParameter.XoffLim = 10;

};

         

DeviceParameter.fAbortOnError = FALSE;

DeviceParameter.wReserved = 0;

         

SetCommState((void *) SerialPort,&DeviceParameter);

         

COMMTIMEOUTS CommTimeOut;

         

GetCommTimeouts((void *) SerialPort,&CommTimeOut);

         

CommTimeOut.ReadIntervalTimeout = (int) (TimeOutInSeconds * 1000);

         

SetCommTimeouts((void *) SerialPort,&CommTimeOut);

Note that a ReadIntervalTimeout is specified, allowing for partial transmissions from a device to be detected.

Also note that this code allows for threaded / overlapping I/O operations on the port.

For more information, see Help\MSHelp\Win32.hlp under "Communications".