Applies To:
  • CitectSCADA 5.xx

Just can't get this dinosaur Model 50 to talk to a serial port on your PC, despite following all the other Citect help and KB articles?

The set-up detailed below worked well from a stand-alone PC COM port over a standard shielded 30 m long cable, finally connected to the Model 50 PLC via a Square D programming cable.

Note: 30 m is well in excess of the maximum recommended cable length for RS 232C.


  • Run Computer Setup Wizard from Citect Explorer. Choose 'stand-alone'.
  • Run Communications Express Wizard from Citect Project Editor.
  • Modify the following defaults under Project Editor - Communications - Ports:

                Port Number: Serial port number of your PC; e.g. '2' for 'COM 2'

                Stop Bits: 2 (not 1)

                Parity: NONE (not EVEN_P)

Check the cable connections:

DB 9 at PC   _______________ DB 25 at PLC
2   _______________ 3
3   _______________ 2
5   _______________ 7
1-4   _______________ 6
7   _______________ 8
jumper 1,4 and 6  --- no connection ---
jumper 7 and 8  --- no connection ---


Note: The shield was not connected at either end, but you may wish to connect one end only to ground.

  • Set the PLC communications parameters (using the Square D programming software - 'UTIL' page) as follows:

                Route: 000 (default)

                Port: Serial port number of your PC; e.g. 'COM 2'

                Baud rate: 9600

Hint: To verify that the communications are physically o.k. you may wish to communicate on-line with the PLC using the Square D programming software. However, if you have a recent model PC, you will have to slow it down with 'SlowDOS' in order to establish reliable communications. The SlowDOS parameter takes a bit of experimenting to suit the speed of your PC.

The following batch files worked well:

            230 MHz Pentium

                cd c:\sy50

                slowdos 6000 c:\sy50\sfw50.exe

            380 MHz Pentium

                cd c:\sy50

                slowdos 10500 c:\sy50\sfw50.exe