Looking for help to end a debate

[dorsetkl]

Hello, new to the forum and looking for some input to end a debate between me and my boss. We have a system using an AB Type 1756-L55/A 5555 Controller, we are having a debate whether or not turning off the controller via the toggle switch on the PS has any effect.

We both agree that to reset the flags in the processor to do the key routine. But the arguement is whether when the key is placed in RUN and the power is cycled to the PLC that there is any effect. I say yes, as I have seen it first hand when cycling the key had no effect, the problem is I do not know why, thus losing my arguement.

Can anyone shed any further light on this debate?

Cheers,
Kevin

 

[HRDDRV]

I think the key routine (Run-Program-Run) will reset any "minor" faults. By cycling power to the processor (no matter what position the key is in) you are basically re-setting it to it's initial startup state. If the battery is good (which is a problem with the L55's) or if you have a memory module, the controller will clear any major faults, reset its internal tag database and be ready to run (depending on key position). If the battery dies and you have no memory module AND you cycle the power you will loose your program...