a/b mem module overwrite protection s:36/10

I have a process PLC5/04 which has recipes that need to be protected. The PLC faulted when a technician shorted out the 24v power supply. I had burned the EEprom but the recipes (older) that had been saved were overwritten when retrievcing the EEprom. Hence, altered (newer) recipes no more!!!!!!!! Disgruntled customer....

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A/B help was vague on the workings of S:36/10.

When your technician shorted out the 24VDC supply, the resulting electrical carnage in the SLC circuitry corrupted the controller's RAM memory, resulting in the CPU clearing the user program and data because the memory couldn't be verified as being intact.

At that time, you had no recipes or logic left. There was nothing to save, retain, or preserve.

The EEPROM did it's job and loaded the program into the SLC memory. It set bit S:36/10 to let you know that it had loaded into an empty memory and was forced to load old data values into memory.

It sounds like that was a hard way to learn that shorting the onboard 24VDC supply of the SLC could result in a cleared memory. If you change your supply to an external one (it wouldn't be very big) that won't happen again.

I was hoping that the lithium battery would give me that warm fuzzy feeling that my RAM was safe.

A/B says:
"
Data File Overwrite Protection S:36/10

Use this bit to determine the validity of retentive data following a memory module transfer. This bit is always set when a memory module to processor transfer occurs with Data File Overwrite Protection selected and protected files are overwritten. Protected files are overwritten anytime a memory module program does not match to processor program at the time of the transfer. This bit is not cleared by the processor.
"
RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002

I have seen the dreaded NVRAM fault before.

My question is if I set the EEprom to always load from EEprom (S:1/11) on power up except for the important data tables (retentive) is this possible ?


A/B says
"SLC 5/03, 5/04 and 5/05
as well as MicroLogix1200 and 1500 Series Bprocessors only You can choose between static or constant protection for data table files on a per file basis. Apply this protection when you create the data file from the Create Data File dialog. Memory module overwrite protection is also available, see MicroLogix 1200 and 1500 above for details."

and also "(For SLC 5/03, 5/04 and 5/05 processors)
Check Constant if you want values in the data table file protected from all changes via communication ports or your ladder program. Check Static to protect data table values from being altered by communication channels. Changes are only allowed by the ladder program during program execution. Check Mem Mod to apply the indicated protection to the memory module. To change the protection for existing files, access the Data File Properties dialog."

RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002

RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002

Judging from the help texts that you provided, you would get the functionality you want.
The program code would allways be loaded from the memory module, the data files would be left untouched.

But I cant see why anyone would want that (*).
If the program is completely missing or corrupted then BOTH program and data files will be loaded anyhow.
If only the program files have an error, then I think that it will be detected by the CPU by the CRC check. That will trigger both program and data to be loaded as well.

I would do something completely different:
Check S:5/8 "memory module loaded on Boot". If set, then reset S:5/8 AND trigger an appropriate alarm message on the HMI, something like "Warning, program was initialised. Check settings, recipes etc."

*: I mean that it wouldnt bring any advantages compared to selecting "load memory module on memory error".