Step7 - SFC83/84 and Flash EPROM with CPU416-3

In my curent project we want to make sure that parameter changes made by the operator during run time and stored in a DB do not get lost if the CPU crashes and has to be rebooted, or if the CPU dies and a new CPU has to be fitted.

With a 300 CPU, this would be no problem - just create an unlinked DB and download it to the MMC then save the new parameters using SFC84 and in the event of a restart, read them back with SFC83 in OB100.

Unfortunately, the sub-contractor is planning to use a 416-3 CPU, which has 256 kB of Load memory (RAM) on board. What I've not been able to figure out is the relation between the external Load memory on the Flash-EPROM and the onboard memory.

In a nut-shell, how can I be sure that the unlinked DB is created on the memory card and not in the onboard RAM?

Bump!

Still haven't got to the bottom of this, although I've picked up a couple more points on the way.

1) Apparently you have to download the complete program to the Flash-EPROM, don't really understand why, since that's not the case with a 300 series CPU and its MMC - I can see that's not going to go down well with the production/maintenance guys!

2) Apparently you can make minor modifications to the program in the onboard Load memory, but that seems to harbour potential for big problems with the program on the EPROM getting out of synch with the actual running program.

Somehow this whole thing is starting to look like a really messy bag of worms - anybody got some more thoughts on it, S7Guy, perhaps?

Cheers

Roy

I use the attached proceedure with S7-400 PLC's.

It is a manual operation but quite straightforward.

Currently stuck in Thailand, trying to get home.

Thanks John, that pretty much confirms the conclusion I had come to, nice to have it in a concise form.

I still haven't been able to dig up any info on the interaction between the on-board load memory and the EPROM. This would be nice to have, to complete the story.

However, in the meantime, it's become academic as the customer has decided against going this route, since he's too worried about minor changes being made and stored in the on-board load memory and not getting transferred to the EPROM.

Once again, thanks for taking the time to post. Hope you manage to get home soon!

Cheers

Roy

What route did he end up going? If he used a RAM card, he would be able to make as many changes as he wants, and he wouldn't have to download the whole program. The only disadvantage is that he had to check the battery very couple of years.

It's not been finally decided yet, but going by what the plant electrical engineer said, it looks like they'll settle for taking a dump of the program every now and again.

This seems to be quite a common approach over here, particularly where shift work is involved. For reasons that I don't fully understand it seems to be impossible to implement a reliable way of handling and documenting program modifications - or at least, it seems to be impossible to persuade all involved to stick to the procedure.

The only thing I can think of is that staff have been cut back so far, that there is absolutely no leeway and they are so overloaded, rushing from one emergency to the next, that their simply isn't time to document and back up stuff properly. Somehow it doesn't seem to fit into the usual picture of hyper-efficient, over-organised Germany!

The disadvantage with the RAM card from my point of view is that if the CPU dies, you can't simply transfer the memory card to the new CPU, like you could with an EPROM card, reboot the CPU and off you go. Personally, I don't see that it's such a major problem downloading the whole program to the EPROM card when you make any changes, it doesn't take that long, after all - but I've already lost that particular battle!