The following code example opens, configures, and closes the serial communications port and performs read/write operations for a TTY terminal emulation application.
/***********************************************************************
Module Name:
port.c
***********************************************************************/
#include <windows.h>
#include "tty.h"
/***********************************************************************
PortInitialize (LPTSTR lpszPortName)
***********************************************************************/
BOOL PortInitialize (LPTSTR lpszPortName)
{
DWORD dwError,
dwThreadID;
DCB PortDCB;
COMMTIMEOUTS CommTimeouts;
// Open the serial port.
hPort = CreateFile (lpszPortName, // Pointer to the name of the port
GENERIC_READ | GENERIC_WRITE,
// Access (read/write) mode
0, // Share mode
NULL, // Pointer to the security attribute
OPEN_EXISTING,// How to open the serial port
0, // Port attributes
NULL); // Handle to port with attribute
// to copy
// If it fails to open the port, return FALSE.
if ( hPort == INVALID_HANDLE_VALUE )
{
// Could not open the port.
MessageBox (hMainWnd, TEXT("Unable to open the port"),
TEXT("Error"), MB_OK);
dwError = GetLastError ();
return FALSE;
}
PortDCB.DCBlength = sizeof (DCB);
// Get the default port setting information.
GetCommState (hPort, &PortDCB);
// Change the DCB structure settings.
PortDCB.BaudRate = 9600; // Current baud
PortDCB.fBinary = TRUE; // Binary mode; no EOF check
PortDCB.fParity = TRUE; // Enable parity checking.
PortDCB.fOutxCtsFlow = FALSE; // No CTS output flow control
PortDCB.fOutxDsrFlow = FALSE; // No DSR output flow control
PortDCB.fDtrControl = DTR_CONTROL_ENABLE;
// DTR flow control type
PortDCB.fDsrSensitivity = FALSE; // DSR sensitivity
PortDCB.fTXContinueOnXoff = TRUE; // XOFF continues Tx
PortDCB.fOutX = FALSE; // No XON/XOFF out flow control
PortDCB.fInX = FALSE; // No XON/XOFF in flow control
PortDCB.fErrorChar = FALSE; // Disable error replacement.
PortDCB.fNull = FALSE; // Disable null stripping.
PortDCB.fRtsControl = RTS_CONTROL_ENABLE;
// RTS flow control
PortDCB.fAbortOnError = FALSE; // Do not abort reads/writes on
// error.
PortDCB.ByteSize = 8; // Number of bits/bytes, 4-8
PortDCB.Parity = NOPARITY; // 0-4=no,odd,even,mark,space
PortDCB.StopBits = ONESTOPBIT; // 0,1,2 = 1, 1.5, 2
// Configure the port according to the specifications of the DCB
// structure.
if (!SetCommState (hPort, &PortDCB))
{
// Could not create the read thread.
MessageBox (hMainWnd, TEXT("Unable to configure the serial port"),
TEXT("Error"), MB_OK);
dwError = GetLastError ();
return FALSE;
}
// Retrieve the time-out parameters for all read and write operations
// on the port.
GetCommTimeouts (hPort, &CommTimeouts);
// Change the COMMTIMEOUTS structure settings.
CommTimeouts.ReadIntervalTimeout = MAXDWORD;
CommTimeouts.ReadTotalTimeoutMultiplier = 0;
CommTimeouts.ReadTotalTimeoutConstant = 0;
CommTimeouts.WriteTotalTimeoutMultiplier = 10;
CommTimeouts.WriteTotalTimeoutConstant = 1000;
// Set the time-out parameters for all read and write operations
// on the port.
if (!SetCommTimeouts (hPort, &CommTimeouts))
{
// Could not create the read thread.
MessageBox (hMainWnd, TEXT("Unable to set the time-out parameters"),
TEXT("Error"), MB_OK);
dwError = GetLastError ();
return FALSE;
}
// Direct the port to perform extended functions SETDTR and SETRTS.
// SETDTR: Sends the DTR (data-terminal-ready) signal.
// SETRTS: Sends the RTS (request-to-send) signal.
EscapeCommFunction (hPort, SETDTR);
EscapeCommFunction (hPort, SETRTS);
// Create a read thread for reading data from the communication port.
if (hReadThread = CreateThread (NULL, 0, PortReadThread, 0, 0,
&dwThreadID))
{
CloseHandle (hReadThread);
}
else
{
// Could not create the read thread.
MessageBox (hMainWnd, TEXT("Unable to create the read thread"),
TEXT("Error"), MB_OK);
dwError = GetLastError ();
return FALSE;
}
return TRUE;
}
/***********************************************************************
PortWrite (BYTE Byte)
***********************************************************************/
void PortWrite (BYTE Byte)
{
DWORD dwError,
dwNumBytesWritten;
if (!WriteFile (hPort, // Port handle
&Byte, // Pointer to the data to write
1, // Number of bytes to write
&dwNumBytesWritten, // Pointer to the number of bytes
// written
NULL)) // Must be NULL for Windows CE
{
// WriteFile failed. Report error.
dwError = GetLastError ();
}
}
/***********************************************************************
PortReadThread (LPVOID lpvoid)
***********************************************************************/
DWORD PortReadThread (LPVOID lpvoid)
{
BYTE Byte;
DWORD dwCommModemStatus,
dwBytesTransferred;
// Specify a set of events to be monitored for the port.
SetCommMask (hPort, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD | EV_RING);
while (hPort != INVALID_HANDLE_VALUE)
{
// Wait for an event to occur for the port.
WaitCommEvent (hPort, &dwCommModemStatus, 0);
// Re-specify the set of events to be monitored for the port.
SetCommMask (hPort, EV_RXCHAR | EV_CTS | EV_DSR | EV_RING);
if (dwCommModemStatus & EV_RXCHAR)
{
// Loop for waiting for the data.
do
{
// Read the data from the serial port.
ReadFile (hPort, &Byte, 1, &dwBytesTransferred, 0);
// Display the data read.
if (dwBytesTransferred == 1)
ProcessChar (Byte);
} while (dwBytesTransferred == 1);
}
// Retrieve modem control-register values.
GetCommModemStatus (hPort, &dwCommModemStatus);
// Set the indicator lights.
SetLightIndicators (dwCommModemStatus);
}
return 0;
}
/***********************************************************************
PortClose (HANDLE hCommPort)
***********************************************************************/
BOOL PortClose (HANDLE hCommPort)
{
DWORD dwError;
if (hCommPort != INVALID_HANDLE_VALUE)
{
// Close the communication port.
if (!CloseHandle (hCommPort))
{
dwError = GetLastError ();
return FALSE;
}
else
{
hCommPort = INVALID_HANDLE_VALUE;
return TRUE;
}
}
return FALSE;
}