LIFO and FIFO

[oldmanraskers]

I have been trying to get to grips with the LIFO and FIFO functions using Compact Logix but it seems that if you have multiple LFL instructions on separate rungs only one item of data is actually put onto the stack - is this how the instruction really works or am I missing something. I expected that each subsequent rung would push something onto the stack?

 

[danatomega]

Get on your instruction (LFL or whatever) and press 'F1' for help on the instruction. At least for LFL it says 'instruction loads one value each time the instruction is enabled' - if the instruction is not dis-enabled, another rung that attempts to enable it will have no effect.

 

[Doug-P]

if the instruction is not dis-enabled, another rung that attempts to enable it will have no effect.

What he said. You will need to do one of two things: a. after each LFL add a rung with an unconditional OTU of the enable bit, or 2. add a rung with an always false input condition going to an LFL identical to the one you've just ENabled. Either of these will reset the enable bit and allow the instruction to see a false-to-true transition.

 

[oldmanraskers]

Thanks for the advice Doug-P That solved my problem.