Applies To:
  • CitectSCADA 3.00

I am having problems establishing reliable communications between a Citect for Windows client machine and a Citect for DOS Scanner. The Scanner either crashes with a "NetBIOS AbEnd" message or doesn't communicate at all.

You may find yourself in the situation where you have a DOS Scanner talking happily to a set of DOS client machines, and merely want to add a Windows client to this system. This is not an easy thing to do and may not even be possible at all, depending on your network architecture. Typically, networked Citect for DOS systems use IPX based datagram communications. Citect for Windows however uses a NetBIOS session based method. Therefore to connect a Windows client you have to install a NetBIOS interface on your Scanner. This can be achieved in two ways. You can switch all your DOS client machines to NetBEUI, establish NETBEUI (remove IPX) on the Scanner and therefore run your network over one protocol only. This may not be suitable for some network systems, as NetBEUI is not routable. The other option is to install the Novell NetBIOS emulator on the scanner to allow the Windows client to talk it using NetBIOS over IPX. This is fraught with peril as the emulator is considered extremely flaky under load, frequently giving rise to abnormal end events. The previously mentioned "AbEnd" message indicates just this sort of problem. The trick here is not to mix network products too much. Loading IPX alongside NetBEUI on the Scanner just doesn't seem to work. They appear to tread on each other's toes somehow and the combination just doesn't agree with the Scanner. Running the Scanner under Windows offers reasonable performance in some circumstances but also seems unreliable.

Also, when you define the units in the Citect for Windows project, ensure the Port field is left blank for IO devices which are derived from the Scanner. If the ports field is not blank then Citect will assume that the I/O Server is a Windows I/O Server. Citect will try to find this Windows I/O Server and when it cannot be found you will get the hardware error '<name> NetBIOS server name not found'.

In general, it would be preferable to use a Citect for Windows IO Server to service both your Windows and your DOS clients.