Greetings.

I have an PFC200 PLC from WAGO (750-8208), which has a RS232 / RS485 port on the front.

I would like to use that port to communicate with an external device using a custom RS485 protocol (i.e. not modbus rtu). I have implemented using the SysLibCom library and tested the protocol code using the simulator. I cannot get the communication to work when connecting the PLC to the device, or even to my laptop via a FTDI RS485 dongle. I suspect that something is not right in the com port setup on the PLC.

Maybe I'm missing something obvious, but I can't see a way to tell SysLibCom that COM0 should be treated as an RS485 port and not a RS232. Can anyone tell me how to do this? Is it even necessary?

My code looks like this:

PROGRAM PT100_PRG
VAR
   sComSettings: COMSETTINGS;
   ePort : PORTS := COM0;
   bIsConfigured: BOOL := FALSE;
   bIsOpen: BOOL := FALSE;
   dwHandle: DWORD;
   dwErrorCount : DWORD := 0;
END_VAR
VAR CONSTANT
   bAddress : BYTE := 0;
   dwErrorHandle : DWORD := 16#FFFFFFFF;
END_VAR
(* implementation starts here *)
IF bIsOpen = FALSE THEN
   bIsConfigured := FALSE;
   dwHandle := SysComOpen(ePort);
   IF dwHandle <> dwErrorHandle THEN
      bIsOpen := TRUE;
   END_IF
END_IF
IF bIsOpen = TRUE AND bIsConfigured = FALSE THEN
   sComSettings.byParity := 0;
   sComSettings.byStopBits := 0;
   sComSettings.dwBaudRate := 38400;
   sComSettings.dwTimeout := 0;
   sComSettings.dwBufferSize := 0;
   sComSettings.dwScan := 0;
   IF SysComSetSettings(dwHandle, ADR(sComSettings)) = TRUE THEN
      bIsConfigured := TRUE;
   END_IF
END_IF
(* ... and some write logic here *)

Thanks in advance.

/Mikkel

Are you sure that it's COM0 not COM1?

Originally created by: scott_cunningham

It is typically a hardware setup, not on the coding side. On some controllers, it is a BIOS setting. Perhaps it is a configuration selection however you setup the hardware (WAGO specific).

Thanks for the inputs. With the help of WAGO support, I found the solution which I'm posting here for future reference.

When using the RS232/RS485 port on the PFC200 module, make sure to:

What tripped me, was using the "wrong" library, not that it was documented anywhere that I could find.

/Mikkel