The 6ES7952-1KM00 is a 4 MB Flash EPROM memory card for SIMATIC S7-400 controllers. It is the most compact FEPROM card that still comfortably holds a complete S7-400 automation program — code blocks, function blocks, data structures, and hardware configuration — without squeezing. For engineers running a mature program on a well-defined machine, 4 MB of non-volatile Flash is the economical sweet spot: enough storage, zero battery maintenance, and the simplest possible BOM.

Who should choose the 4 MB FEPROM card?

OEMs shipping a standard program across multiple identical machines. Maintenance teams managing a fleet of S7-400 controllers where the program has been stable for years. Engineers who value simplicity — no battery to replace, no runtime write complexity, no special download procedures beyond the standard STEP 7 workflow. If your compiled project fits in 4 MB today and your machine's control logic is mature, this card will likely serve the full remaining life of the controller.

What do I give up by choosing FEPROM over RAM?

Two things: online program changes and CFC online monitoring. FEPROM cards require the CPU to be in STOP mode for program downloads — you cannot modify code blocks while the process is running. RAM cards (6ES7952-1A series) support RUN-mode downloads and are required for CFC online monitoring in PCS7 environments. If your application runs a batch process or continuous production line that cannot be stopped for program updates, a RAM card may be the better fit despite the battery maintenance requirement.

Frequently Asked Questions

How do I check if my program fits in 4 MB?

In STEP 7, open the project properties and check the compiled block size. The total size of all code blocks, data blocks, and system data must be under 4 MB. Note that the S7-400 CPU's built-in work memory is separate — the FEPROM card stores the load memory image, not the runtime work memory.

Can this card be read in a Siemens programming device?

Yes. Insert the FEPROM card into a compatible PG with a memory card slot to view, archive, or duplicate the user program without connecting to the CPU.