PLC 5 memory

Hi Gents,


Just wondering if someone would know exactly what happens if one tries to download a fresh copy of a program to a PLC 5/15 CPU while the back plane swicth no 8 is set to ON .according to the manual this switch prevents you to clear the memory of the CPU. I am just wondering if the download does clear the memory? isn't the new program going to the memory?

To me if you put a fresh program into a CPU whos memory has been possibly corrupted that download should clear the memory.

If this statement is true than how is it possible that when you try doing a download to a PLC5 CPU which is in a rack with dip swicth 8 in the ON position the download appears to go through normally without any issue.Shouldn't that give a big warning or error message saying download not possible memory clear protection ON?

Could someone explain how that works?

As far as I remember you get an error message.
The message was a bit misleading, something along "diagnostic error" and a hex code.
The program will not be cleared.

To me if you put a fresh program into a CPU whos memory has been possibly corrupted that download should clear the memory.

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Not cleared. You will download the configuration, program files and data files from your offline project.

If this statement is true than how is it possible that when you try doing a download to a PLC5 CPU which is in a rack with dip swicth 8 in the ON position the download appears to go through normally without any issue.

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Are you sure about this ?

I once had the previously mentioned error message when trying to download a modified program, and after much scratching of head I decided to check the memory prtect switch. And it was indeed set to on.

Hi Jesper,

Well I checked it 10 times. There is no error message. The program or memory is somehow corrupted as after flicking switch 8 over and doing another download the remote rack and the Remote I/O free light came on instantly after placing the CPU into run mode. While with Switch 8 ON there was no way to get the remote rack working even after downloading multiple times.
There was no message at all so I had no way of knowing whether the program download did or did not get through.
Maybe the CPU is actually faulty.I don't have another CPU to try offline off site. This small issue in a real world live situation is a perfect booby trap.
The CPU has been removed to perform a Software platform upgrade. I did remove it from the rack (12 slot) and replaced it with a 1771 ASB / B adapter. Configured the CLogix bridge and commissioned the I/O with no issues. Upon return to the old PLC5 platform to restart production(new platform software not 100% ready)the dip swicthes from both local rack and remote rack have been put back EXACTLY as they were before they've been touched. On power-up the PLC5/15 faulted. Could not get online to check the fault. Was able to reset with the key switch.After many hours of downtime and troubleshooting got the idea to start right from scratch and set the system up as it would have been set up the first day when it was installed. For that I did check the position of all the switches on the local rack and I was horrified to see that the position of 6 & 7 was set as such the program will be loaded from EEPROM on start-up if no program or corrupted program found.The only problem is that this PLC didn't have an EEPROM. Never had.
So what I think happened is that I pulled out the CPU kept it powered down for 6 hours and something got corrupted as such on power up six hours later it prompted the rack to "force" a load from the EEPROM. There is no EEPROM so the CPU faults.i tried to download a fresh copy of the program but switch 8 has been also set ON so that should not allow a download or at least that should not allow the clearing of the corruption which prompted the EEPROM load. At least without giving an Error message.

I just don't understand how the PLC5/15 program got into the PLC5/15 if switch 8 is set ?

I think this is a perfect booby trap.

I cannot explain what you have observed regarding switch 8.

Since the PLC5/15 is the classic generation, maybe the behavior is different to the enhanced CPUs that I have had experience with.

You can also go online check S:2/15 for the memory protect switch status. Try to change the switch position, and see if that is reflected in the online status.

not sure whether this will help with your problem, but here's a quick experiment that I just ran on my lab equipment ...

I put the chassis DIP switch number 8 in the ON (memory protected) position for a PLC-5/20E system... then I reinstalled the processor and tried to do a regular download ... I got the popup message shown below ... (note that the processor already contained a working program – which I was not allowed to overwrite) ...

suggestion: if you can get online with the processor, take a look at the "Switches" tab available from the Status file ... this shows what the processor is seeing when it "reads" the chassis DIP switches ... the information there might be helpful to you ...

TIP: do NOT trust similar information which might appear in the "IO Configuration" area of the software ... the information there is merely "documentation" and is subject to human entry errors ... the "Switches" tab is much more reliable ...

I just don't understand how the PLC5/15 program got into the PLC5/15 if switch 8 is set ?

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just a guess: maybe the switch was OFF (unprotected) – and the original program was downloaded ... then the processor was pulled and the switch was changed to ON (to protect the processor from an inadvertent download/clear operation) ... then the processor was reinserted ...

again – this is just a guess - but that could account for the switch being ON ...

good luck with your project ...

.

Hi Ron,

This is also what I think. The download has been done with the swicth in the Off position then CPU out switch ON CPU back then Run. I think in my case the CPU is faulty. I cannot get that CPU to service the local Rack only the remote rack. Luckily the actual production process only requires the remote I/O rack. Unfortunately nobody (including me ) knew that the moment I disconnected the CPU for the first time. The actual input led's on the input cards were on as you'd expect but no output light was on which was normal as well as the process/production was stopped. However I didn't realize that the output card "active" lights are not on. On none of the output cards.
I actually took some pictures 8 months ago (when scoping the project) and looking back through those pictures and zooming in I realized that the output cards "active" lights are not on. I also realized that the I/O on that rack is not actually needed for the process as production has been cut back as a consequence less machinery is used and by shear luck the machinery used is driven by the top rack.
The CPU doesn't have any fault and it appears all ok.I strongly believe that the CPU is faulty and part of that fault is that it cannot see the Backplane Memory Protection DIP switch as well as it cannot service the local I/O on the local rack.

something else just occurred to me ...

The CPU has been removed to perform a Software platform upgrade. I did remove it from the rack (12 slot) and replaced it with a 1771 ASB / B adapter.

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DIP switch 8 on the chassis backplane takes on a DIFFERENT function when a 1771-ASB remote I/O adapter (rather than a PLC-5 processor) is installed in the chassis ... is it possible that during the switchover the DIP switches got scrambled? ...

just guessing – but maybe that could account for your confusion with the switch settings ...

I once saw a crew of guys on a startup operation waste the better part of two days – simply because they were using the instructions from the PROCESSOR book – rather than the bookd for the remote I/O ADAPTER that they were trying to install ... again – the DIP switch settings are DIFFERENT depending on which component is being installed ...

TIP: before moving any DIP switches, I personally always write down the "as found" positions – just to prevent any confusion about how to get back to where I started ...

Hi Ron,

No no no. Definitely didn't get them scrambled. I was aware that there are different settings for the same switch depending what is in the Rack CPU or 1771 ASB adapters. I wrote everything down and even took pictures.

This was a time bomb. The PLC5/15 has been downloaded to with the switch 8 off than the switch back to on. Had to be.

The other part of the story is that swicthes 6 & 7 were also wrong as they were vset as such to load the program from the EEPROM in case of failure .The only small issue is that there is no EEPROM in that PLC5/15 but the previous CPU which was in the rack before this PLC5/15 had an EEPROM(PLC5/25).

So memory gets corrupted on the PLC5/15 .On power up tries to load from the EEPROM.There is no EEPROM so there is a fault. Cannot access the CPU for some reason while faulted. Clear fault with key switch go online but no indication of any issue.No racks are working.Neither local nor remote. Try to download and download goes ok no error message. Obviously still the same corrupted program.

Flick switch 8 after a few hours of going round and round download program and remote rack is ok instantly.

Local rack is not ok but if a different CPU is used (CPU 5/30) both rack come up as expected and everything works.

For the actual process in the machine (funnily enough) there is no need for the local rack to service any I/O so the rack being out of use CPU faulty goes under the radar undetected.

Very bad day.

I have the PLC5/15 running the plant with one rack faulty(been like that for 8 months as I found some old pictures I took and when I zoomed in the output active light is not on on any output cards. I just didn't notice that then as everything was working and I was just taking pictures to quote for the upgrade.

Thanks for your replay Ron. Really appreciate your time.

I have the PLC5/15 running the plant with one rack faulty(been like that for 8 months ...

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that's good news ... now slowly - slowly - walk away ...

I am well clear already. d[-_-]b

I'm still just wondering ...

the next time you get a chance to go online (or maybe just take a look at a recent offline copy of the program) it might be interesting to see if any of the bits shown in the figure below just happen to be set to a ONE status ...

when I tried the setting shown on my lab system, I got the indications that you've reported ... specifically, the processor continued to scan its program – but the output module's "ACTIVE" indicator was OFF – even though the module's bits on the output image table were being driven OFF and ON by the program ... all of the outputs on my output module were turned OFF – in spite of the fact that the processor was in the RUN mode ...

note that I'm talking about an output module located in the LOCAL (processor resident) chassis ... I won't be able to try this experiment with a REMOTE chassis until later today ...

personally, I've never seen these particular bits used for ANY reason – and I have a hard time imagining why someone would change their settings ... still – SOMETHING is causing your system to act weird – and while it certainly COULD be a defective processor, I'm inclined to suspect something more along these lines ...

any chance that you could post your entire RSP file? ...

.

Hi Ron,

Just had a look. Those bits are not set. However some of the inhibit bits are set.Please have a look.