Siemens S7 Memory Cards

[odonnea2]

We use S7 400 PLCs on our site, together with 1MB Falsh EPROM cards and battery backup installed. The PLCs were supplied by the vendor with this configuration.
We also however have an offline backup database to store all our master PLC programs, therefore if a PLC is to be restored (in the event of a hardware failure) we would do this from the offline master PLC file.
My question is this. Before preceeding to restore we would perform a memory reset on the PLC. I understand that by doing this the contents of the flash EPROM are automatically copied to the CPU RAM? Does this automatic copy happen while the CPU is in STOP mode. If this is the case this would mean that in order to restore the CPU with the master program from our offline database then I would have to write the program to the flash EPROM first using "PLC>Load user program onto memory card" and then perform a memory reset to load the program into the CPU via the memory card?
Can you advise. Thanks.

 

[Ken M]

My understanding of how these Siemens PLCs operate is that when you switch to RUN, they first check to see if an EPROM is installed. If not they attempt to run whatever is stored in their working memory. If an EPROM is installed they first copy its contents in to working memory, and then continue to run what is now in working memory.

If you've had to make a CPU change because of hardware failure, then the EPROM from the old CPU should still hold the config/code/data etc and can be used in the new CPU. Plug it in the new CPU before power-up, let it power up, and then go to RUN. I think you can also request manually that the working memory is loaded from the EPROM in STOP, but that requires you to be online.

 

[odonnea2]

Thanks Ken_M

I was searching back through the previous threads related to this and found the following thread and a response by you as follows
http://www.plctalk.net/qanda/showthread.php?t=17377&highlight=Siemens+Memory+Card

"There are two portions of load memory : the built-in part on every CPU (which is often quite small, say 8Kb or so), plus the add-on portion. If you add a RAM card to the S7-400 to expand the built-in load memory, this is additive, so you get 8KB plus whatever you added. If you add an EEPROM card to the S7-400 to expand the built-in load memory, this is replacement, so the built-in load memory no longer gets used."

However I have one further question. When the "PLC>Download" function is used in Simatic Manager to download a single modified block, this block is transferred to the integrated load memory (RAM). However does this also need to be downloaded to the Flash EPROM using "PLC>Download User Program to Memory card"? Otherwise on the next power cyle if the backup battery was dead, or following a memory reset, then an older version of the program would be loaded from the EPROM.
Am I correct here?

http://www.plctalk.net/qanda/showthread.php?t=17377&highlight=Siemens+Memory+Card

 

[Ken M]

Wow, I don't remember writing that. Well found. I hope I was correct!

My understanding of your third paragraph is exactly like yours. Consider the EPROM to be the main source of data & code. If you or anyone else makes changes to code in RAM, then their responsibility must always be to ensure that these changes are reflected in the EPROM.

Ken

 

[John Gaunt]

I use the attached proceedure to write S7-400 program to Flash Memory Cards. It saves current setpoints, limits and other set-up information as well as the program. For my purposes it has replaced the need to save and restore these values from Citect SCADA as I did in the past.

Of course it is necessary to ensure that backups are done following program changes or significant changes to the production set-up.