S7 318-2 Memory Question

Hello,

I noticed a few weeks ago every time I try to download a data block to my 318-2 processor, I get a message saying I need to compress the memory. I have 512KB EEprom card now. If I try to download a data block or function block without first making a memory reset, the blocks will not download and I get the message (cannot copy block). If I do memory reset and then download the whole PLC program it works again. Can you help me to understand a little bit about this memory in Siemens processors. I have old 318-2 processor. Below is the memory I copied and pasted so you can see the problem. It shows the Load Memory RAM is 97% full. Every time I try to download some changes to PLC I have to make a memory reset in order for it to go without any errors. How do I free up this load memory?

Thanks for your help!

PK


Thanks,



Paul Kemp

This is from memory (no pun intended), so I can only tell you what I remember without being completely certain.
With some S7-400 CPUs you had to use a RAM card in stead of an EEPROM in order to utilise all of the available memory. I remember that I had an S7 414-3 CPU that needed such a RAM card to go beyond a certain memory limit.
I think that the RAM card was only necessary for when you had to make online changes to the program. For normal operation, it was OK with the EEPROM card.
Changing between RAM card and EEPROM card is such a nuisance that I used the RAM card all the time. That meant of course that the battery backup was absolutely critical.

As a 318 CPU is really a S7-400 CPU in S7-300 clothing, it could be that the same applies.

It looks like almost all blocks (program and data) are located in RAM memory not in EEPROM. You can download them to EEPROM by selecting "PLC->Download User program to Memory Card". After this operation only chnges will be downloaded to RAM memory and 64kB shoud be quite enough for small corrections. During download all blocks (SDB,DB,FB,FC) are written to EEPROM.

The load memory needs to have enough space to hold a copy of the DB (The current download operation). Once downloaded, it will overwrite the origional DB. Hence for a period of time, there are 2 versions of the DB in the load memory. Then the DB pointer list is updated to point to the new one and the old is lost.

Sorry i took so long to respond. Yes you were right. I used "PLC->Download User program to Memory Card" and that freed up the memory so I don't have the issue anymore. Thanks for your help!

PK