The 6ES7952-1AH00 is a 256 KB RAM memory card for SIMATIC S7-400 controllers — the smallest RAM card in the S7-400 family and the most compact path to online program change capability on the platform. Despite its modest capacity, it delivers the full RAM feature set: RUN-mode downloads, online block modifications, CFC chart monitoring, seamless integration with the CPU's internal load memory into one contiguous area, and SFC-based runtime data block access. A backup battery or external backup voltage is required.

What fits in 256 KB on an S7-400?

A lean, focused program. Think of the simplest S7-400 applications — a small valve sequencing loop, a basic motor start/stop with a few interlocks, a single control loop with minimal data overhead. Many early S7-400 installations were commissioned with programs that fit comfortably in 256 KB and have not changed substantially in decades. This card is also used as a spare or replacement part for legacy S7-400 systems where the original RAM card was this capacity and the program has never outgrown it.

Why would you choose a 256 KB RAM card today?

Three scenarios. First, exact replacement — your existing S7-400 has a 256 KB RAM card, the program fits, and you need a like-for-like spare. Second, ultra-compact new deployment — you are commissioning a minimal S7-400 application and know the program will stay small. Third, cost — the 256 KB card is the most economical entry into the RAM ecosystem for S7-400. For any program approaching or exceeding 200 KB in compiled size, step up to the 1 MB card (6ES7952-1AK00) for headroom.

Frequently Asked Questions

Does this card work with modern STEP 7 versions?

Yes. The 6ES7952-1AH00 is recognized by all current versions of STEP 7 and PCS7. The card's interface has not changed — a 256 KB RAM card from the current production line works identically to one manufactured decades ago.

What is the difference between this card and the older 64 KB RAM card (6ES7952-0AF00)?

Capacity — 256 KB versus 64 KB. Both are RAM cards with identical feature sets, voltage requirements, and form factor. The 1AH00 replaces the 0AF00 as the entry-level RAM offering for S7-400.