AB PLC 5 RIO Config problem for the experts

Hi guys, I haven't been on for quite awhile, but spent my day getting frustrated by a PLC with a couple of remote racks and I'm wondering if any of you have a clue to how to figure this one out.

We have a PLC with 2 separate 16 Slot chassis, with racks up to 3/7. The configuration file is not accurate and shows racks 2 & 3 in separate 8 slot chassis. Even with this everything that is configured in the system works up to Rack 3 Slot 3. I found in the Channel B Remote I/O configuration that it was only setup to communicate to 1/2 the rack. When I set it to full rack like just like rack 2 is, it faults and won't communicate past 3/3. When I auto-config it picks 1/2 of a rack.

I added an OFE2/B to slot 4 of rack 3, setup the BTR/BTW and was getting an error -11 meaning it couldn't establish comms with the module. That is how I discovered that I couldn't configure the rest of the rack in the Channel B RIO configuration.

In the status file I don't have anything there inhibited, the only 1 on the whole "racks" page was the fault I created trying to get it to full instead of 1/2.

I'm sure I'm missing something here as I haven't had to configure these very often and I'm sure hoping one of you has had the same issue. I'm a little worried to change the current IO configuration page to match the physical chassis layout as I don't want to create any problems with the 24/7 gas plant this PLC runs.

Thanks,
Cory

Some of the "I/O Configuration" window elements in RSLogix 5 are only for documentation purposes and don't necessarily have to reflect the actual configuration of the RIO Scanner port. I use PLC-5's seldom enough to not remember perfectly.

The window that matters is the Channel Configuration window, titled "Edit Channel Properties". This is where you can perform Autoconfigure, and this is where the real configuration of the RIO scanner channer resides.

The "I/O Configuration - Chassis Table" does not have to reflect real hardware, so long as the logical arrangement is right.

A single 16-slot chassis is frequently two logical 8-slot "racks" of I/O memory.

I'm not sure about why the last four slots don't seem to work. It might have something to do with the DIP switches on the backplane... time to go read a bit...

DIP switch S2-4, "SCAN" feature

The 1771-ASB Series C has a DIP switch, S2-4, labeled "Scan".

The User Manual describes the "Scan" setting:

"On for all but the last 4 slots
Off for all slots"

That is consistent with what you describe; take the 1771-ASB out and inspect it.

Info from Publication 1771-um001, page B-9.

Thanks Ken, I'm pretty sure the dip switch on the ASB module is the answer. I'll have to wait until I can pull it out but it probably is set to to not scan the last 4 slots, based on it's behavior. You are awesome. We have the Power supply in the last 2 slots but I'm sure that shouldn't matter for scanning purposes. I'll have to read more to find out why they even have that option in there.

Thanks again.

Follow-up

The Dip Switch was the problem in my situation. Thanks again Ken!