dmargineau: Side cars can do CIP E/IP messaging if the card, and the processor are the right revision. Rockwell AnswerID 7983, 61405,66899 have more details.
Processor has to be minimum Series E, Rev D.1, Series D rev E.1, Series C, rev N.1 (This is valid for PLCEs as well).
Sidecar has to be Series A rev D or higher, or any Series B or higher (Series C being the one with RJ-45 and 100Mbps support).
I have messaged between PLC-5 with sidecar and ControlLogix (which has to be CIP because AFAIK ControlLogix can't do PCCC ethernet messaging), but I've never done Ethernet IO direct from PLC5. My understanding it's technically possible, but extremely un-recommended, and there's a lot of manual work to it.
I have an engineering company claiming they've done it before with VFDs, and want to start our PLC5-CLGX migration that way: replace 20-COMM-R cards with 20-COMM-E cards, controlled by the PLC-5 over the existing sidecar. I'm curious to see how they did it, purely to see that it can be done, not because I want it.
I've had luck with migrations in the past where we start moving RIO racks and drives to Ethernet IO controlled by a CLGX, and the IO table is messaged to and from the CLGX which essentially acts as a mailbox. Once all the IO is migrated, the process control logic is moved to the CLGX. Care has to be taken to handle message timeouts, as the standard timeout is unacceptable for IO.