A communication class for serial port

Tuesday Feb 8th 2000 by Remon Spekreijse

A communication class for serial port

In the newgroups there are many questions about serial communication so I thought: make it public! It's freeware. The only thing I expect from users is that they drop me a mail. All modifications on this class are free, but please let me know if it solves a bug or adds some good features. Also comment your code and don't let me solve your bugs!


The class is not intended to use as a baseclass for modemcommunication but more for driving hardware or reading hardware via the serial port.

From the classes included there is only one class important: CSerialPort. The other classes are only there to illustrate the use of this class.


In your software you only need to create an instance of the CSerialPort class and call InitPort.
// the owner (CWnd) of the port (receives message)

BOOL CSerialPort::InitPort(CWnd* pPortOwner,  
 UINT  portnr,   // portnumber (1..4)
 UINT  baud,    // baudrate
 char  parity,   // parity 
 UINT  databits,   // databits 
 UINT  stopbits,   // stopbits 
 DWORD dwCommEvents,  // EV_RXCHAR, EV_CTS etc
 UINT  writebuffersize) // size of the writebuffer

The dwCommEvents flag can be used for communication with the owner of this class.

The flags can be one of the following (or combined with |):
  • WM_COMM_BREAK_DETECTED A break was detected on input.
  • WM_COMM_CTS_DETECTED The CTS (clear-to-send) signal changed state.
  • WM_COMM_DSR_DETECTED The DSR (data-set-ready) signal changed state.
  • WM_COMM_ERR_DETECTED A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY.
  • WM_COMM_RING_DETECTED A ring indicator was detected.
  • WM_COMM_RLSD_DETECTED The RLSD (receive-line-signal-detect) signal changed state.
  • WM_COMM_RXCHAR A character was received and placed in the input buffer.
  • WM_COMM_RXFLAG_DETECTED The event character was received and placed in the input buffer.

Accept the first parameter all parameters are optional. The standard values are:

portnr  = 1
baud  = 19200
parity  = 'N'
databits  = 8, 
stopsbits = 1, 
dwCommEvents = EV_RXCHAR | EV_CTS,
nBufferSize = 512);

So the follwing code is enough to make communication possible:

in the header of the owner:

 CSerialPort m_Serial;

in the code:


Then the tread that watches the port is started and all events on the port are send to the owner. The receive a character the owner needs a messageentry in the messagemap:

BEGIN_MESSAGE_MAP(CCommtestDlg, CDialog)
and they must be handled:
LONG CCommtestDlg::OnCommunication(WPARAM ch, LPARAM port)
 // do something with the received character

 return 0;

This is it for reading. Writing can be done with WriteChar or WriteToPort


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