The 6ES7952-1AL00 is a 2 MB RAM memory card for SIMATIC S7-400 controllers. It extends the CPU's internal load memory into one contiguous RAM pool, enabling RUN-mode program downloads, online block modifications, and CFC chart monitoring — all without interrupting the process. A backup battery or external backup voltage is required to preserve the card's contents through power cycles.

2 MB of RAM — what is the use case?

A focused S7-400 program that needs online change capability. Think of a machine cell controller, a small batching system, or a packaging line where the core program is compact but the process cannot be stopped for every program tweak. An S7-400 CPU with 1–2 MB of internal load memory paired with this card provides 3–4 MB of total contiguous RAM — enough for the application code, data blocks, and a modest recipe set. The 2 MB RAM card delivers the full flexibility of the RAM platform at the lowest practical capacity point for most real-world S7-400 programs.

RAM at 2 MB vs. FEPROM at 2 MB — how do I decide?

The capacity is the same. The decision is entirely about your engineering workflow. If your program is final and you want the lowest-maintenance installation — no battery, no monitoring, no scheduled replacement — choose the FEPROM card (6ES7952-1KL00). If you need to modify code online, monitor CFC charts in real time, or are working in a validated PCS7 environment where online engineering is required, choose this RAM card. The cards are physically interchangeable; the choice is about how you work.

Frequently Asked Questions

How long does the backup battery last with this card installed?

The S7-400 backup battery typically lasts 1–2 years depending on ambient temperature and the specific CPU model. The CPU diagnostics buffer provides early warning when the battery voltage drops. Siemens recommends annual preventive replacement. The RAM card's backup current draw is in the microampere range — it does not significantly affect battery life compared to the CPU's own draw.

Can I use SFC82/83/84 to read and write data blocks on this card at runtime?

Yes. The system functions SFC82 (CREATE_DB), SFC83 (READ_DBL), and SFC84 (WRIT_DBL) can access data blocks stored in the RAM card's load memory from within the user program. This is a standard technique for recipe management and data logging on S7-400 systems with RAM load memory.