Procedure ControlRTS;
Var
 S: String;
 lDCB: TDCB;
 fHandle: THandle;
Begin
 S:='COM1';
 // open port
 fHandle:=CreateFile( Pchar(S), GENERIC_READ Or GENERIC_WRITE, 0,
 Nil, OPEN_EXISTING, 0, 0);
 If fHandle=INVALID_HANDLE_VALUE Then
 Begin
 // can't open....
 Exit;
 End;
 // read settings
 If Not GetCommState( fHandle, lDCB) Then
 Begin
 // can't read
 Exit;
 End;
 // Fill dcb
 lDCB.BaudRate:=CBR_2400;
 lDCB.ByteSize:=8;
 lDCB.Parity:=NOPARITY;
 lDCB.StopBits:=ONESTOPBIT;

 // !!! we will manage RTS ourself !!!
 ldcb.Flags:=(ldcb.Flags And $FFFFC0FF) Or $00000100;
 // set comm state
 SetCommState( fHandle, ldcb);

 // Here we can manage
 // Reset RTS
 EscapeCommFunction( fHandle, CLRRTS);
 // Set RTS
 EscapeCommFunction( fHandle, SETRTS);

 // Close port
 CloseHandle(fHandle);
 fHandle:=0;
End;