The 6ES7952-1AM00 is a 4 MB RAM memory card for SIMATIC S7-400 controllers. It combines with the CPU's internal load memory to form a single, contiguous storage pool — the CPU addresses the card and internal memory as one unified volume. This architecture enables RUN-mode program downloads, online block modifications, and CFC online monitoring, all without transitioning the CPU to STOP. A backup battery or external backup voltage (EXT.BATT) is required to preserve data through power cycles.

RAM at 4 MB — who is this card for?

PCS7 users running compact to moderate process control applications where online engineering access is a daily requirement. An S7-400 CPU with 4 MB of internal load memory paired with this card provides 8 MB of total contiguous load memory — enough for a typical PCS7 project with CFC charts, SFC sequences, and a standard process object library. For non-PCS7 applications, 4 MB of RAM also suits any S7-400 program where the engineer needs the ability to tweak code without shutting down — a dosing loop, a temperature control strategy, a conveyor routing change.

What maintenance does a RAM card require?

One thing: the backup battery. The S7-400 CPU's internal battery (or an external supply connected to EXT.BATT) must provide continuous backup voltage to the RAM card whenever the system is powered off. Siemens recommends replacing the battery every 1–2 years. Many S7-400 installations monitor battery status through the CPU diagnostics buffer, which will issue a warning well before the battery voltage drops below the retention threshold. If the battery does fail during a power-off period, the RAM card loses its contents and a full program download is required on the next power-up.

Frequently Asked Questions

Does this card support S7-400H redundant systems?

Yes. Each CPU in an H-system pair requires its own RAM card. Both cards must be identical in capacity — you cannot mix a 4 MB RAM card in one CPU with an 8 MB card in the other.

Can I convert from a FEPROM card to this RAM card without changing the program?

Yes. The program is the same — only the storage medium changes. Power down, swap the FEPROM card for the RAM card, power up, and download the program. The CPU will address the RAM card as part of its unified load memory. Note that you will now need to maintain the backup battery.