AB PLC Analog Input Module 1771 IFE - locking up


Thread Starter


We have a PLC5 with a new analog input card added to it---this PLC is on remote IO. There are two PLC's controlling this one area in our plant. Anyway the analog input card (1771 IFE) just locks up and quits reading our tank levels. To correct it ---or get the analog card to start reading levels again the maintenance tech toggles power on the other remote rack! I can't find anything being sent from the remote rack that would step on the level data in this rack but I can't figure out what toggling power on the other rack does to this analog card either. Any ideas?? I read in a forum somewhere of a similar problem but can't find the article! HELP!! :0)

Bob Peterson

In certain older vintages of AB racks there is a known bug with using IFE cards in remote racks that exhibits this problem when continuous mode is used on the block transfer read instruction.

I don't ever set these BTR instructions to continuous mode, and use a N/C BTR done bit to reset the BTR instruction.


Peter Hasler

Hi All

If you are using the RIO protocol, the AB 1771-IFE Card needs to be written to in a cyclic fashion to refresh the configuration data of the module. If you have multiple analog cards this should be done in a staggered fashion by using the "Done" or "Error" bit from the preceding BTR/BTW to trigger the next write job.

This solved the problems I had when migrating from PLC 5 To ControlLOGIX

Hope this helps
How is your read and write block transfer being accomplished? Are you using the status bits from the control of the write and the read block transfer to enable the transfers? Check your program to verify there is no errors with your transfer. Here is an example -paste this into rslogix5.

rung 1:XIO N33:0/15 XIO N33:5/15 BTR MODULE:-1 001 4 0 N33:0 N10:0 12 NO

rung 2:XIO N33:5/15 XIO N33:0/15 BTW MODULE:-1 001 4 0 N33:5 N20:0 37 NO



It sounds like you are running out of resources on the Remote I/O network. That's a programming problem, but it would be difficult to explain all
possible scenarios by email.

If you send the RSP file to me directly (the A-List can't allow attachments), I'll take a look and post my observations to you and the

Hope this helps!

Larry Lawver
Rexel / Central Florida
(ScienceOfficer @ compuserve.com)
Is the analog card being read through a RIO adapter? We had a machine that one day decided to quit transfering data from a BT module in a remote rack. We were still getting all of the digital I/O to work. Finally after two days of head scratching, we found that the old adapter module didn't support the type of block transfers we were using. Somehow it managed to work for the first eleven years anyway! We replaced the adapter with a newer revision and it was fixed...

Daniel L. Parker

Assuming the block transfer programming is correct and is done according to the manual, the module is susceptible to lockup from the differences in voltage on the input signals. The IFE module has only +/-15V of isolation between channels. If your field devices are all four-wire transmitters, try some analog signal isolators. With regard to the BT programming, make sure the BTW is driven by the first scan bit (S:15/0?-it's been awhile!) so that the module is reconfigured each time the controller starts. Also, make sure the BTW is driven by the BTR status bit for the unconfigured state of the module (bit 15 of the first BTR status word?-it's been awhile!)
The common mode suggestion sounds like a good one.
I'd be curious to know what happens if you swap
the IFE cards, rack-to-rack. Also, I'd want to
know if the remote I/O cable is properly terminated, not grounded, etc. Same with the
remote chassis grounds, etc.