I/O not responding

Is there any nondestructive bit that is set when a remote I/O is not responding?
I'm wanting to program in a preemptive warning and controlled process stop when i lose network connection to a remote I/O device.
1756-L72 controller using Ethernet IP for remote point I/O

I'm no expert, but I found your question interesting to me as well. I don't know what remote i/o block you have, but for anyone using aentr series with compact logix plc on rs logix 5000 or studio 5k, the manual shows these options under slot status in the i/o section under controller tags.

I also saw in the controller properties some "fault bit" options under minor faults tab, but unsure what these do or how they relate.

Yes. The status bits for the individual point I/O racks/cards might be useful. Let me ask you a really dumb question now. Looking at several different status words for different racks, I have some that display VALUES for the bits and some that don't. The column is grey. What gives?

Oh wow. I closed tags window, and reopened it and they show now. IDK?? Told you it was stupid.

The status bits of any I/O device won't automatically go bad when the device stops communicating. Those status bits are sent by the device itself, so if the device stops sending them, well, they'll stay in whatever state they were last in.

To check for an I/O device being connected or not, you can use a GSV on the Module object and the EntryStatus attribute. If it returns 16384 (decimal) or 4000 (hex) then the module is connected; every other result indicates a problem of some kind.


More info here (techconnect required) and here (no techconnect required). Or, search the Logix Designer help for the GSV instruction and the Module object. That goes through all the different status information you can get back from a module fairly comprehensively.

I've seen that effect where live values are grayed out; I'm still not sure if it's an artifact of my older software or not.

For modular I/O like POINT and FLEX, there is a Status bit array that's part of the Input assembly for the Adapter itself. Each bit represents the status of a module in the POINT or FLEX installation.

Rockwell was clever with those; the I/O connection itself is broken, then all of the bits are 1, so the value of the whole DINT is -1.

For devices that don't have status bit arrays, you monitor the I/O connection (usually over EtherNet/IP). The standard method is to use a Get System Variable (GSV) instruction to read the EntryStatus attribute of the Module object, and divide the resulting Integer (INT, not DINT) tag by 4095 to get a value between 1 and 8.

A value of 4 means the I/O connection is established and operating, and any other value means that it's broken, or shutting down, or waiting for re-establishment.

There are a lot of examples of that on this Forum. There are also examples in the various Programming Manuals for ControlLogix; I want to say this would be in 1756-PM014 or 1756-PM015.

Ken Roach said:

For modular I/O like POINT and FLEX, there is a Status bit array that's part of the Input assembly for the Adapter itself. Each bit represents the status of a module in the POINT or FLEX installation.

Rockwell was clever with those; the I/O connection itself is broken, then all of the bits are 1, so the value of the whole DINT is -1.

Click to expand...

Huh, I stand corrected. I knew that the status bits would update if a particular module went bad, but I thought we were still relying on the connection to the fieldbus adaptor to tell us about it, meaning if we just lost comms to the (e.g.) 1734-AENT, the status bits would all just stay the same!

Guess that simplifies a few things for me...

ASF said:

The status bits of any I/O device won't automatically go bad when the device stops communicating. Those status bits are sent by the device itself, so if the device stops sending them, well, they'll stay in whatever state they were last in.

To check for an I/O device being connected or not, you can use a GSV on the Module object and the EntryStatus attribute. If it returns 16384 (decimal) or 4000 (hex) then the module is connected; every other result indicates a problem of some kind.


More info here (techconnect required) and here (no techconnect required). Or, search the Logix Designer help for the GSV instruction and the Module object. That goes through all the different status information you can get back from a module fairly comprehensively.

Click to expand...

+1...that's how its done.

OK so here is my solution. I created an EQU comparing the binary feedback from the I/O status word, to the Binary signature it should be receiving in normal operation, so that if any module fails to send back anything other that what is being compared, it will send an alarm and commence a controlled stop to the process at its inception. Simplicity is always best! Thanks for all your input.