Tye Canadian company SST- Technologies offers several gatway solution that you could use. I am sure they have a Modbus to DataHighway Gateway or Modbus to some other AB network such as devicenet
Call Allen Bradley, they make a ModBus communication card that goes in the SLC slot. It may be made by Prosoft, but it is listed with Allen Bradley. I installed one of these comms cards in a SLC chassis to read some temperature meters via MODbus.
NOTE: When I did the install, the documentation had the wiring for Modbus reversed, which took me a couple days to figure out. Be wary of the wiring diagrams.
There is a way which we have used several times. We purchased a Prosoft 3150-MCM Modbus communications module for the SLC5 series. It's expensive and has a cumbersome programming method but works ok. Check Prosoft website.
It is possible to communicate SLC processors with MODBUS protocol by using BM95 Multiplexer and a SA-85 PC based card (in your PC) and writing a programme in C and converting it into an EXE file and downloading in the BM95 Multiplexer.
We had tried it in our project wherein we established communication between Allen Bradley PLC-3/10 and our SCADA ( PROWIN - Taylor Industrial Controls) in MODBUS PLUS protocol using BM95 and SA-85cards and a C programme.
