Applies To:
  • CitectSCADA

I have an Allen-Bradley device. RSLinx can see it but can Citect communicate with it? Which Citect driver should I use for communication? 

Currently Citect has two drivers that communicate with RSLinx directly, via it's API. The first is an OPC client driver that talks to RSLinx's OPC Server. The second is the ABRSLINX driver which connects to RSLinx's API. Both drivers require a full version of RSLinx. I.e. RSLinx OEM or Gateway, with software activation.

Both drivers can be used to connect to basically any device that RSLinx can communicate with but here some thoughts to consider.

  • OPC is a string addressed based protocol and thus there is no advantage in using this protocol to connect to PLCs that do not support string based addressing. At present the Allen-Bradley's Controllogix type processors are the only ones that support this.
  • You can connect to the Controllogix processor with the ABRSLIINX driver but you will have to set up the Controllogix in PLC5 emulation mode. This is achieved by mapping registers of the PLC into arrays, then giving these arrays PLC5 type data file names. E.g. An array of integers, Array_Int[1000] can be mapped to the N7 data table. Citect then reads the array from N7:0 to N7:999 as per a PLC5. (NB. I have not checked the maximum size). As a down side though you lose the added functionality of the PLC's complex data structures, so I do not really see an advantage in this method.
  • The OPC driver can still be used to connect to PLC5s etc, but as they do not support string based addressing there does not seem to be an advantage here. Also, status tags are not supported which means there may be problems with redundancy.

My preference would be to use the OPC driver for the Controllogix processor and the ABRSLINX driver for the other processors.