CPU 312 — panel fit and memory ceiling
The Siemens 6ES7312-5AC82-0AB0 is an S7-300 CPU 312 with 6 kbyte integrated RAM (2 K instructions, where 1 instruction averages 3 bytes). It runs on 24 V DC and draws a typical power loss of 9 W including the integrated I/O. The MPI interface is present, supporting S7 communication as server. The CPU fits a single rack (max. 1 rack) and measures 80 mm wide by 125 mm high by 130 mm deep — it occupies one standard S7-300 slot width on the DIN rail.
Temperature range and environmental limits
The lower limit accommodates unheated storage or cold-start conditions; the 60 °C ceiling is typical for enclosed panels without forced cooling — above that, derating applies.
Lifecycle — end-of-life stage
For a BOM freeze or replacement project, confirm the required memory and interface profile — the S7-300 family offers CPUs with larger work memory and PROFINET interfaces that may serve as functional replacements.
Integrated memory and retentivity
The 6 kbyte integrated RAM includes a retentive area of 72 bytes (memory bits, times, counters, data) that holds without battery. The software clock is present; a battery option is not required for retentivity of that 72-byte block. The command set covers binary logic, bracketed operations, arithmetic (fixed and floating point), counting, shifting, rotating, and block calls — sufficient for medium-complexity machine control.