What can cause AB PLC5 to go into program mode?

Is there anything that can cause a PLC5 to switch to program mode then back to run mode, other than someone switching to prog mode with either software RSL5 or turning key switch?

Background: Yesterday I got called in. Through our historical trending I eventually found that the root cause of the upset was one of the PLC5s going into program mode for 4 minutes then back to run mode. It was back to run mode before I arrived. One electrical tech on site at the time. Says he was no where near the PLC or prog software. I've known him for 10+ years and I have no reason to doubt him. RSL5 could have been open on a pc accessible to anyone (control room, shop, etc), but these folks (12 on shift operators) are just not like that, to fiddle with this stuff. Our 5s are accessible through our corporate network via CLX ENBT and DHRIO bridges. We do not use firewalls (long story) or programming passwords.

You could programatically place the PLC in program mode with ladder. However you could not switch it back out of program mode into run mode because the program would no longer be running. Another PLC could do it over a newtork, and RSView can also be configured to change a PLCs mode (I do this myself in RSView apps from a diagnostic screen that allows a tech to clear a PLC fault and restart the PLC.)

Alaric,

I did not know that RSView could be used to switch a PLC from Run to Progarm mode. Would you give some more details on that subject?

This could be way off, since I HAVE NEVER SEEN A PLC5 DO THIS. BUT, I had a SLC5/04 put itself in program mode randomly about once every 10 to 48 hours for a week before I gave up on all other possiblilties and replaced the CPU. It never happened again. That machine, however, stayed in program mode and did not switch back into run mode on its own. I suspect that it's keyswitch had a physical problem.

That PLC5 has a similar keyswitch doesn't it? Just a WAG, but ya never know, unless it continues long enough to test a variety of theories...

If it keeps happening it will be worth noting the effect (if any) of the keyswitch position. My guess is that this is a one time deal and we'll never know for sure what happened...

In order for an outside process to put the machine in program mode programmatically, someone would have to go to a bit of trouble, and I seriously doubt that actually happened. Doesn't make it impossible, but it would be at the bottom of my list of suspects.

Even though all the techs are trustworthy, it's possible one of them inadvertently caused the problem or is embarrased or fearful of admitting it. Then again, Willie Gates could be to blame...I can't count the number of times a windows based program did **** to me that I was unaware of because of screen update latency or other stupidity that goes on with modern PCs running MSBloatware...

JMHO
PEC

Lancie1 said:

Alaric,

I did not know that RSView could be used to switch a PLC from Run to Progarm mode. Would you give some more details on that subject?

Click to expand...

All you have to do is write to tags that use the status bits. Instead of reading the "RUN" and "PROGRAM" status, you could write to the same bits.

I just looked in the program I'm working on, and yes, somebody thought it would be a good idea to monitor S1/1, and S1/3. If you can read 'em, you can write 'em...

I think somebody was "midnight operating" and clickieoopsed in the wrong place. I suggest passwording anything that might give access to PLC functions, even diagnostics.

I don't use the word "impossible" much.

There is no known hardware, firmware, or software mechanism that will cause a PLC-5 controller to autonomously go from RUN to PROGRAM and back to RUN.

Either this was caused by an unintentional RSLogix 5 operation or the controller wasn't really in PROG mode but rather was powered down and then rebooted.

An easy diagnostic and preventative is to simply go turn the keyswitch all the way left into hard RUN mode (and then hide the key). No programming or visualization software can cause the controller to change modes when the keyswitch is in RUN mode.

Is the PLC5 key in the keyswitch?

We remove them as a practice. That way we know that one must knowingly want to change the state - and only by having a key with them.

Fault mode is also consider as program mode, the PLC 5 went in to fault mode the visualization software will detect this as a program mode??? is it so!!!

tomalbright said:

Lancie1 said:

Alaric,

I did not know that RSView could be used to switch a PLC from Run to Progarm mode. Would you give some more details on that subject?

Click to expand...

All you have to do is write to tags that use the status bits. Instead of reading the "RUN" and "PROGRAM" status, you could write to the same bits.

Click to expand...

Thats right. I have a few PLCs that are in foreign plants where there is no one on the maintenance staff that has enough PLC experience to trust that they would be able to solve PLC problems. So I put in some extensive diagnostic screens in RSView - and one screen allows them to view the processor status, clear a fault code, and place the PLC back into remote run (provided the key is in REM), as well as set the processor time. It is simply a matter of creating the RSView tags to read/write from/to the status file bits. I also added the RSLadder (ladder viewer) Active X to a diagnostic screen so that they can view the running ladder from withing RSView, and with a small bit of VB programming there is a password protected button that allows a re-download of the program to the PLC. I don't normally put those features into an RSView app, but in this case it has saved me at least one trip across the pond.

Thanks for all the feedback fellas.

Ken Roach said:

...or the controller wasn't really in PROG mode but rather was powered down and then rebooted.

Click to expand...

Historical trending (WW InSQL & ActiveFactory) shows the processor clock (S:23) continued to run during the 4 minutes that S:01/01 (run mode) went low so I've ruled out a power loss.

Oakley said:

Is the PLC5 key in the keyswitch?

Click to expand...

Yes, and they're all set to rem prog mode

rPraveenkum said:

Fault mode is also consider as program mode, the PLC 5 went in to fault mode the visualization software will detect this as a program mode??? is it so!!!

Click to expand...

Will the clock continue to run?

wildswing said:

Will the clock continue to run?

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processor clock will continues run even processor mode is in Program mode since processor operation is based up the processor clock

when the processor is in program mode the RTC will not stop

But what about the fault condition that you said would look like program mode. Will the clock continue running then? I just checked and neither fault words S:10 or S:11 changed before, during or after those 4 minutes. S:10 = 16386 ("dh+ node table has changed" and "arithmetic overflow"), S:11 = 0.

you are also logging the S:10 or S:11 data in the visualization software?

rPraveenkum said:

you are also logging the S:10 or S:11 data in the visualization software?

Click to expand...

Yes