Logix CPU Faulted, could not get online?

Hello,

I had an instance today where a L55 processor had faulted. I had to access this site remotely, and could ping the Ethernet Module, but could not see it with RSLinx.

I managed to instruct the op on site to cycle power to the PSU, and this allowed me to finally get online to the CPU. Once online, there was a major fault on the processor, indicating that there was a major un-recoverable fault, with no-program in the CPU.

I was able to clear the fault, download the last saved copy of the code, and everything returned to normal, so all good.

The issue is, what could of caused this fault? I thought that you could still get-online with a faulted CPU via Ethernet? The CPU and ENBT module are v16.20, with the ENBT module in slot 9, and the CPU in Slot 1.

Normally you can see what the faults are, are they all cleared on power cycling?

That model of controller and that firmware revision are a red flag; there was a bug in several revisions of 1756-L55 controller firmware that would cause a nonrecoverable fault on a bogus RAM failure. It was fixed in versions 15.05 and 16.21.

The notifications went out a couple of years ago but it sounds like this controller might have eluded upgrade.

RA Knowledgebase Document 45709 describes the problem, the patch, and the upgrade.

Thanks Eddie,

Interesting, I never knew about this. We only actually updated the CPU to V16.20 from V13 in about 6-10 months ago, after having problems with the ENET module and remote IO. I will make a point of visiting site as soon as I get the chance to update all the firmware to 16.21.

Saying that, does that also explain why I could not get online to the CPU via Ethernet?