Absolute encoder on controllogix

Can I use an 1756-IB16 input card to process the grey code from an Electro-Cam absolute grey code sourcing encoder?

Probably, yes.
It depends on the speeds you need to update, but if you are just reading positions, it should work.

A "sourcing" encoder is likely compatible with the 1756-IB16 inputs, which are conventionally thought of as "sinking" because you apply +24V DC to them.

The principal trick to getting Gray code to work reliably on 1756 series modules is to use a Synchronous Copy (CPS) instruction to copy the data out of the module into a holding register before decoding it. This prevents the module's RPI from possibly updating in the middle of the Gray decode logic.

Examples of Gray code -> integer logic can be found in the RA Knowledgebase article 32743 (TechConnect Required).

I would use the simple Structured Text loop described in that document. You could even embed it into an Add-On Instruction if you like.

Thanks Ken. That was exactly the info I was looking for. Time to go confuse the **** out of my boss.

Ken, the RSLogix version I was using for the project didn't have Structured Text, but I was able to use ladder logic to convert the Grey Code to Binary using the Knowledge Base article you linked. Using the CPS instruction, there is actually much less logic needed using the absolute encoder than the old incremental encoder. The new routine hads4 rungs, as compared to over 30 on the old routine. The only downside I could tell was that the resolution of the old encoder was 2000 cycles per revolution, as compared to a max of 255 on the absolute encoder.

Another thing I was wondering...when I called ElectroCam to see if they had information about which module they recommended using, they seemed to have no information at on on ControlLogix, even though they had example logic and module information for the SLC right in the documentation included with the encoder. Should I call and share the information with them, or keep it to myself?