SLC CPU 5/05 Powers Up in Download Mode

LadderLogic

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Join Date
Jun 2003
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Chicagolandia
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Guys:

It's been a very long while since I worked with an SLC500 PLC so my question is for those of you who are current. This morning I encountered a strange problem I cannot seem to find a fix for.

A PLC with 5/05 CPU (firware rel. OS10, I beleive) would not switch to "Run" mode upon power-up although the keyswitch is in "Run" position and the program and the data are valid and the Ethrenet communications work.

When looking into the processor status with RSLogix, there are no faults and the CPU is in "Download" mode (???). The only way to reset this condition is to flip the keyswitch into "Prog" and then back to "Run" - after which everything works just fine.

I tried cycling the power several times, and every time it was precisely the same.

Is there a setting that controls how the CPU would power-up? Or is this some strange bug? I was not able to find any information on the web yet so maybe someone knows.

Thanks in advance.
 
just a guess - but I'd start by taking a look at the settings highlighted below ... the Help button does a fairly good job of giving an overview of what the settings do ...

if this doesn't help, consider posting your entire RSS file ...

good luck with it ...

.

startup_protection.PNG
 
Another SWAG, does it have a memory module?

If so try it without the memory module. Or make sure the module has a good backup of the current program.
 
Last edited:
Thanks for your suggestions, I do not have a copy of the file in front of me but will take a look. There is no memory module installed and no error codes are displayed, sorry.
 
I saw something similar once with a 5/04 that would occasionally put itself into PROGRAM mode as if someone had flipped the keyswitch. It was in Remote RUN mode at first. This only happened once every couple of days. Leaving the key in run mode did not help. Swapping power supplies didn't help. Replacing the CPU fixed it. I assumed that there must have been something physically wrong with the keyswitch like a damaged trace or contamination. That one got a big red X on it and stayed parked in the office after I pulled it from production.

I am not sure I follow what you mean by "Download Mode".
 
Last edited:
Another WAG: I would try re-downloading the project to the PLC. Maybe on the last download comm's were lost at the last second, or something didn't get put back in program mode. That bit might be showing up every power-up.
 

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