Windows + SetCommState how to set RTS? - visual-studio-2012

Question

I have an application that has been ported up from VC++ 6 where it worked fine. The code in question uses the WinAPI for a serial device driver. When ported to VS2012, the same code behaves rather differently.
Create a DCB, set SetCommState and go. CTS was set high, RTS was set high and you were on your way.
Since ported up to VS2012 Pro MFC, I am finding that it sets up SetCommState the same with or without hardware flow control:
memset(&dcb, 0x00, sizeof(dcb));
dcb.DCBlength = sizeof(DCB);
// Must be TRUE, only binary mode in Windows
dcb.fBinary = TRUE;
dcb.fParity = FALSE;
// XOn/XOff disabled
dcb.fTXContinueOnXoff = TRUE;
dcb.fOutX = FALSE;
dcb.fInX = FALSE;
dcb.XonLim = 0;
dcb.XoffLim = 0;
dcb.XonChar = 0;
dcb.XoffChar = 0;
// Misc Stuff
dcb.EofChar = 0;
dcb.EvtChar = 0;
dcb.ErrorChar = 0;
dcb.fErrorChar = FALSE;
dcb.fNull = FALSE;
dcb.fAbortOnError = FALSE;
// 8N1 Setup
dcb.ByteSize = 8;
dcb.Parity = NOPARITY;
dcb.StopBits = ONESTOPBIT;
// Baud Rate
if (dwBaudRate == BAUD_115200)
{
dcb.BaudRate = CBR_115200;
}
else
{
dcb.BaudRate = CBR_38400;
}
// setup hardware flow control
if (bHardware == eYesHardwareFlowControl)
{
// ================ FLOW CONTROL ON ================
switch (bIgnoreCTS)
{
case eIgnoreCTS:
dcb.fOutxCtsFlow = FALSE;
break;
case eEnableCTS:
dcb.fOutxCtsFlow = TRUE;
break;
default:
case eCTSDecideLater:
dcb.fOutxCtsFlow = TRUE;
break;
}
// DSR Flow Control
dcb.fDsrSensitivity = FALSE;
dcb.fOutxDsrFlow = FALSE;
// <<Hardware flow control On(TRUE) Off(FALSE)>>
dcb.fDtrControl = DTR_CONTROL_ENABLE;
// <<Hardware flow control On(_HANDSHAKE) Off(_ENBLE)>>
dcb.fRtsControl = RTS_CONTROL_HANDSHAKE;
}
else
{
// ================ FLOW CONTROL OFF ================
switch (bIgnoreCTS)
{
case eIgnoreCTS:
dcb.fOutxCtsFlow = FALSE;
break;
case eEnableCTS:
dcb.fOutxCtsFlow = TRUE;
break;
default:
case eCTSDecideLater:
dcb.fOutxCtsFlow = FALSE;
break;
}
// DSR Flow Control
dcb.fDsrSensitivity = FALSE;
dcb.fOutxDsrFlow = FALSE;
dcb.fDtrControl = DTR_CONTROL_ENABLE;
dcb.fRtsControl = RTS_CONTROL_ENABLE;
}
if (SetCommState(m_hIdComDev, &dcb) == WINDOWS_API_ZERO_IS_BAD)
{
dwLastError = GetLastError();
}
At this point, I have set up the DCB, cleared it. I don't read in the previous state is I don't want to trust any garbage of anyone that previously used the port. Then I set up every field with Baud, Flow Control and CTS Ignore being the only optional items.
So, what I've noticed is that I can create situation where the Device and the PC don't communicate. Now, mind you, they always did before and they always work with Hyperterminal, ProComm, TeraTerm and so on. What I can see is that when these comm programs start (and the old VC++ 6 App), when the device is created and set up, RTS is immediately set high.
Now, my App, once the DCB is set up, SetCommState called; RTS is always LOW. And when this happens, communications is toast.
I want to FORCE RTS to be high and thought I could do it like this:
if (EscapeCommFunction(m_hIdComDev, CLRRTS) == WINDOWS_API_ZERO_IS_BAD)
{
dwLastError = GetLastError();
}
if (EscapeCommFunction(m_hIdComDev, SETRTS) == WINDOWS_API_ZERO_IS_BAD)
{
dwLastError = GetLastError();
}
But this fails, it gives an error 87 (parameter error). And I cannot quite figure it out. Even if I just SETRTS high only, it fails.
Any ideas on how I can force Windows to set RTS high after I setup the comm parameters in the DCB?

Answer 1

Well it turned out to be a device problem and not a windows problem at all.