Re: com port communication with a device

Here is some code I used to interface with foot-pedals which used the  
protocol lines, but the general design is similar to handling data  transfer.
 
procedure TStatusThread.Execute;
var
hComm :  THandle;
DCB : TDCB;
OLStatus : TOverlapped;
Reslt, TmpInt : DWord;
TimedOut : boolean;
begin
FreeOnTerminate := true;
try
try
hComm :=  0;
{open the comm port as a  file}
hComm :=  CreateFile(PChar(PortName[CommSelf.FPort]), GENERIC_READ or  
GENERIC_WRITE,
0, nil,  OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL or FILE_FLAG_OVERLAPPED,  0);
if hComm = INVALID_HANDLE_VALUE  then
raise  EPortError.Create(
Format('Failed to open %s port : Error  %d',
[PortName[CommSelf.FPort], GetLastError]));
{modify the comm port protocol to give us a "switch supply  voltage"}
GetCommState(hComm, DCB);  //  get port existing setup
with DCB do  begin
{although we don't send  & receive data, the DCB settings are  not
implemented on the comm  port unless the data parameters are  set}
BaudRate :=  CBR_19200;     // set some baud  rate
ByteSize :=  8;
Parity :=  NOPARITY;
StopBits :=  ONESTOPBIT;
DCBlength :=  SizeOf(DCB);
{this are flags to  set our "switch supply voltage"}
Flags := (RTS_CONTROL_ENABLE shl  12);
// shl 12 positions the  RTS_CONTROL_ENABLE flag in the other flags
end;
if not SetCommState(hComm, DCB)  then  // change the settings
raise EPortError.Create(Format('SetCommState Failed : Error  %d',
[GetLastError]));
{these are the protocol  signals to monitor for our "switched inputs"}
SetCommMask(hComm, EV_CTS or EV_DSR or  EV_RLSD);
{note : Don't use EV_RING, it is not  detected in Win 95 - MS KB Q137862}
OLStatus.hEvent := CreateEvent(nil, true, false, nil); // to watch the  port
if (OLStatus.hEvent = 0)  then
raise  EPortError.Create(
Format('Failed to create overlapped event : Error  %d',
[GetLastError]));
TimedOut := false; // set  here to cause initial WaitCommEvent()
repeat
if not TimedOut then // set  an event monitor
WaitCommEvent(hComm, FCommEvent,  @OLStatus);
{now wait for the  event or a timeout}
Reslt :=  WaitForSingleObject(OLStatus.hEvent,  300{mS});
case Reslt  of
WAIT_OBJECT_0 : if  GetOverlappedResult(hComm, OLStatus, TmpInt, false) then  
begin
{a comm event has occurred - check the line status  ...}
GetCommModemStatus(hComm,  FModemStatus);
{... and indicate the status on the  form}
Synchronize(HandleCommEvent);
{... and trigger a fresh event  monitoring}
TimedOut :=  false;
end {if GetOverlappedResult(etc  etc)}
else
raise  EPortError.Create(
Format('Error in overlapped status : Error  %d',
[GetLastError]));
{end; if GetOverlappedResult(etc etc)  else}
WAIT_TIMEOUT :  {start the watch again - event monitor is still  valid}
TimedOut := true;
else  begin
raise  EPortError.Create(
Format('WaitForSingleObject failed : Error  %d',
[GetLastError]));
Terminate;
end;
end; {case  Reslt}
until Terminated;
finally
CloseHandle(OLStatus.hEvent);
CloseHandle(hComm);
Terminate;
end;  {try / finally}
except
on E: Exception  do
ShowMessage(E.Message);
end; {try / except}
end;

Alan Lloyd



   


[Non-text portions of this message have been removed]



 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/Delphi-JEDI/

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/Delphi-JEDI/join
    (Yahoo! ID required)

<*> To change settings via email:
    mailto:[email protected] 
    mailto:[email protected]

<*> To unsubscribe from this group, send an email to:
    [email protected]

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/