Hello,

I have S7-300 PLC + 64KB memory card. I'm little confused about PLC memory. In TIA Portal project resources I found different memory areas - load and work. I understand that work memory is PLC's, but that is load memory? Should I choose my memory card's size in load memory?

Now I have 64KB memory card and my project uses 94% of load memory, but I can't transfer project changes to PLC, because I get error, that where is not enough space. I tried to load empty project to PLC, but in online monitoring I saw that 14% of load memory is still used.

Can somebody explain me this and tell if it is possible to reset load memory?

Best regards.

Hello Mn;

You could start by reading the following document, and look at the available links, to have a general idea of the way memory is structured in a S7-300 CPU, and distinguish load and work memory areas:

How can you obtain an overview of the memory concept of SIMATIC S7-300 CPUs and C7 devices?

Your situation will depend on the exact part number (MLFB) of your CPU, depending on the age of the CPU it will use either a MC (RAM or EPROM) or a MMC as load memory.

As a rule of thumb, the ration of load to work memory should be at minimum 1 to 1:5. That is a 64 kB memory card would be adequate for a CPU having 48 kB work memory; only very old S&-300s have that small a work memory.

So please provide the MLFB of the CPU you want to use so we can help out. I would also be useful if you attach a screenshot of your memory settings, from the CPU properties, in HWConfig (runtime), and the type and size of the presently used memory card.

Hope this helps,

Daniel Chartier

Hello, Daniel,

Thank you for reply. CPU's part number: 6ES7 314-1AG14-0AB0. It's a new PLC, we bought it few months ago.

MMC: 6ES7 953-8LF30-0AA0 64KB.

Best regards.