Configuring a Communications Resource

The following example opens a handle to COM1 and fills in a DCB structure with the current configuration. The DCB structure is then modified and used to reconfigure the device.

 

/* A sample program to illustrate setting up a serial port. */

 

#include <windows.h>

 

int

main(int argc, char *argv[])

{

  DCB dcb;

  HANDLE hCom;

  BOOL fSuccess;

  char *pcCommPort = "COM2";

 

  hCom = CreateFile( pcCommPort,

                     GENERIC_READ | GENERIC_WRITE,

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

                     NULL, // no security attributes

                     OPEN_EXISTING, // comm devices must use OPEN_EXISTING

                     0,    // not overlapped I/O

                     NULL  // hTemplate must be NULL for comm devices

                     );

 

  if (hCom == INVALID_HANDLE_VALUE) {

      // Handle the error.

      printf ("CreateFile failed with error %d.\n", GetLastError());

      return (1);

    }

 

  // We will build on the current configuration, and skip setting the size

  // of the input and output buffers with SetupComm.

 

  fSuccess = GetCommState(hCom, &dcb);

 

  if (!fSuccess) {

      // Handle the error.

      printf ("GetCommState failed with error %d.\n", GetLastError());

      return (2);

    }

 

  // Fill in the DCB: baud=57,600 bps, 8 data bits, no parity, and 1 stop bit.

 

  dcb.BaudRate = CBR_57600;     // set the baud rate

  dcb.ByteSize = 8;             // data size, xmit, and rcv

  dcb.Parity = NOPARITY;        // no parity bit

  dcb.StopBits = ONESTOPBIT;    // one stop bit

 

  fSuccess = SetCommState(hCom, &dcb);

 

  if (!fSuccess) {

      // Handle the error.

      printf ("SetCommState failed with error %d.\n", GetLastError());

      return (3);

    }

 

  printf ("Serial port %s successfully reconfigured.\n", pcCommPort);

  return (0);

type

............

  TComPortHwHandshaking = ( hhNONE, hhNONERTSON, hhRTSCTS );

  TComPortSwHandshaking = ( shNONE, shXONXOFF );

 

  TPacketMode = ( pmDiscard, pmPass );{ What to do with incomplete (incoming) packets }

 

  TComPortLineStatus = ( lsCTS, lsDSR, lsRING, lsRLSD);

  TComPortLineStatusSet = set of TComPortLineStatus;

........

 

const

  dcb_Binary              = {text}000001;

  dcb_ParityCheck         = {text}000002;

  dcb_OutxCtsFlow         = {text}000004;

  dcb_OutxDsrFlow         = {text}000008;

  dcb_DtrControlMask      = {text}000030;

  dcb_DtrControlDisable   = {text}000000;

  dcb_DtrControlEnable    = {text}000010;

  dcb_DtrControlHandshake = {text}000020;

  dcb_DsrSensivity        = {text}000040;

  dcb_TXContinueOnXoff    = {text}000080;

  dcb_OutX                = {text}000100;

  dcb_InX                 = {text}000200;

  dcb_ErrorChar           = {text}000400;

  dcb_NullStrip           = {text}000800;

  dcb_RtsControlMask      = {text}003000;

  dcb_RtsControlDisable   = {text}000000;

  dcb_RtsControlEnable    = {text}001000;

  dcb_RtsControlHandshake = {text}002000;

  dcb_RtsControlToggle    = {text}003000;

  dcb_AbortOnError        = {text}004000;

  dcb_Reserveds           = $FFFF8000;

 

var

 dcb: TDCB;

..............................

dcb.Flags := dcb_Binary;

  { Enables the DTR line when the device is opened and leaves it on }

  if fEnableDTROnOpen then

      dcb.Flags := dcb.Flags or dcb_DtrControlEnable;

  { Kind of hw handshaking to use }

  case FComPortHwHandshaking of

    { No hardware handshaking }

    hhNONE:;

    { No hardware handshaking but set RTS high and leave it high }

    hhNONERTSON:

      dcb.Flags := dcb.Flags or dcb_RtsControlEnable;

    { RTS/CTS (request-to-send/clear-to-send) hardware handshaking }

    hhRTSCTS:

      dcb.Flags := dcb.Flags or dcb_OutxCtsFlow or dcb_RtsControlHandshake;

  end;

  { Kind of sw handshaking to use }

  case FComPortSwHandshaking of

    { No software handshaking }

    shNONE:;

    { XON/XOFF software handshaking }

    shXONXOFF:

      dcb.Flags := dcb.Flags or dcb_OutX or dcb_InX;

  end;

type

  _DCB = packed record

    DCBlength: DWORD;

    BaudRate: DWORD;

    Flags: Longint;

    wReserved: Word;

    XonLim: Word;

    XoffLim: Word;

    ByteSize: Byte;

    Parity: Byte;

    StopBits: Byte;

    XonChar: CHAR;

    XoffChar: CHAR;

    ErrorChar: CHAR;

    EofChar: CHAR;

    EvtChar: CHAR;

    wReserved1: Word;

  end;

  fDCB.Flags := fDCB.Flags or aCOMProp.RTSControl or aCOMProp.DTRControl;

const

  { DTR Control Flow Values. }

  DTR_CONTROL_DISABLE = 0;

  {$EXTERNALSYM DTR_CONTROL_DISABLE}

  DTR_CONTROL_ENABLE = 1;

  {$EXTERNALSYM DTR_CONTROL_ENABLE}

  DTR_CONTROL_HANDSHAKE = 2;

  {$EXTERNALSYM DTR_CONTROL_HANDSHAKE}

 

  { RTS Control Flow Values}

  RTS_CONTROL_DISABLE = 0;

  {$EXTERNALSYM RTS_CONTROL_DISABLE}

  RTS_CONTROL_ENABLE = 1;

  {$EXTERNALSYM RTS_CONTROL_ENABLE}

  RTS_CONTROL_HANDSHAKE = 2;

  {$EXTERNALSYM RTS_CONTROL_HANDSHAKE}

  RTS_CONTROL_TOGGLE = 3;

  {$EXTERNALSYM RTS_CONTROL_TOGGLE}