Micrologix 1400 Timer Issue

[black07dub 0]

I'll preface this with, I'm an Omron guy, that was what I was trained on. Took a new job with new challenges with AB. I've been able to navigate them so far but this has got me stumped. I'm currently programming a RFID badge reader to my trainer setup for the later introduction to the plant. My issue is with something that seems to simple to be a problem. A timer. My issue is the timer is started and counts up to the target number and then just resets to 0. Never triggers the DN bit. I'm sure this will be something stupid but I'm at a loss here. I'll attach the program via link. https://ibb.co/K7VXbC1

 

Thanks,

Don

[Joe E. 259]

The DN bit is indeed turning on...for  1 scan. When the TON finished, the DN bit turns on. On the very next rung, the DN bit being on turns on B3:57/1. On the next PLC scan, with the memory location B3:57/1 containing a "1", the XIO instruction becomes false, which drops the EN input of the TON instruction, which resets it.

For a really good treatment of the PLC scan cycle and how to decipher what's going on, see these Youtube videos:
https://www.youtube.com/playlist?app=desktop&list=PLGzS56y9k4eYr1uS3jPPxGunBTtPcS3Ez

 

 

[black07dub 0]

So the issue I just found is the compare statement. I had nothing to MOV 0 into that destination. So even though I'm not seeing the DN bit turn on, the statement is just restarting the timer because of it. I moved the DN bit to trigger a MOV instruction of 0 into N7:30 and it worked correctly. I guess I needed to see someone explain what I knew differently.

Thanks for the link Joe!