RSLogix 5000 FIFO Issue

Hi everyone,

Im installing a machine at a customer now and ran into an issue that i havent run into before.

I have a fifo setup to open 1 of 6 valves (one at a time).

The fifo works fine under normal conditions, however when pressing an E-Stop the fifo seems to load only 1 of the 6 valves.

Attached is a picture of the loading sequence.
After i clear the e-stop all the requests are made and the FFL is called 3 times in rung 1, 2 and 3 simultaneously.

For some reason only the first position is filled with value 1. The other 2 rungs are actually run as i tested this with latching test bits at the end of them.

Please note that i have tested to make sure it doesnt unload the other positions.

What i think is causing the issue is the FFL is trying to load the values on the same position.

Is this true and is there any way to fix this?

You need to somehow make the control word .EN bit go false between each rung. Instructions with a control register need to see the false-to-true transition to do their thing.

One possibility - unconditionally unlatch the .en bit before each FFL instruction.

Doug-P said:

You need to somehow make the control word .EN bit go false between each rung. Instructions with a control register need to see the false-to-true transition to do their thing.

One possibility - unconditionally unlatch the .en bit before each FFL instruction.

Click to expand...

That seems to solve the problem indeed. Thanks a lot!

What i also tried before your suggestion is after every FFL instruction move the POS in a temp dint. And at the end of the routine move a 0 into that temp. Then before the loading condition compare the POS to the TEMP value.

That seemed to work aswell but it would load the 2nd valve after cycling to the whole program once.

Your solution is a lot cleaner.