🚀 go-pugleaf

Hi all,

Using BCB 6 & WIN2K

I have created my own com port class and have had no problems transmitting
and recieving data via my serial ports, but now I want to control the RTS
line as a direction control pin for RS485 data. After checking the
documentation I found that I should be able to use the following:

void __fastcall TCommPort::SendData(String dta)
{
 if (dta.Length() == 0)
     return;

 DWORD NOBW;
    SetCommMask(hComm,EV_TXEMPTY);

    if (RS485)
     Set485(true);

 WriteFile(hComm,dta.c_str(),static_cast<DWORD>(dta.Length()),&NOBW,NULL);

    DWORD evt;
    while (evt != EV_TXEMPTY)
    {
     WaitCommEvent(hComm,&evt,0);
    }

 if (RS485)
     Set485(false);
}

void __fastcall TCommPort::Set485(bool b)
{
 RTS = b;

 if (IsOpen)
    {
     if (b)
      EscapeCommFunction(hComm,SETRTS);
        else EscapeCommFunction(hComm,CLRRTS);
    }
}


In the SendData function I set a comm event to fire when the tx buffer is
empty, I then place the data into the queue in the serial port, and the wait
for the TX buffer empty event to occur, when this happens I place the RTS
line low again.

Unfortunately, the WaitCommEventFunction returns immediately and the RTS
line is dropped straight away, does anyone know what I've done wrong, or how
to control the RTS another way so that it drops after my data is sent.

I cant use the fRtsControl from the DCB structure as it drops the line upto
10 ms after the data has been sent and is not fast enough.

TIA

Joe