Writing to Discrete Inputs

My customer has a PLC5 program that writes zeroes to a series of discrete inputs (I registers) when a fault is detected in that remote rack. We are upgrading them to CLX and I was wondering if this is still possible in Controllogix.

Thanks.

You should be able to set the fault behavior of each channel to do whatever you want (go True, go False, keep last value, etc.)

If you could specify the type of rack the remote I/O is in, and even communication format, folks here could provide more definitive answers.

In general, Logix based controllers scan the I/O asynchronous to the program scan, so I always buffer my inputs regardless so that the data doesn't change mid-scan. If you buffer your inputs, you could use a GSV to verify the status of your remote rack adapter and clear the appropriate input buffer data in the event of a rack fault.

The remote rack is an ASB communicating to the PLC via Remote I/O. It has always been my experience that discrete I/O will just change back to its native state unless you force the change. I don't have enough experience in Logix to know if it operates differently.

In general, when an I/O connection to a module fails, A-B platforms leave the Input data table or tags in the last state they were in before the failure.

A broken I/O connection is the only instance in which you can write a value to an Input tag and not have it over-written on the next cyclic data update.

So yes, you can detect an I/O device connection failure with a GSV and write zeroes to the Input tag.

I am always skeptical of code that manipulates the Input data table in this way: why would you intentionally erase the knowledge of the state the inputs were in at the time of failure, when you could retain that information and use the Connection Status to inform your control system of the connection failure ?