Memory and retentivity
Work memory is 4,096 bytes max. Retentive data is supported but must be restarted at each restart. Forcing is supported, and the variables that can be forced include inputs, outputs, memory bits, DBs, times, and counters. Useful for commissioning, but remember that forcing overrides the program — tag it in your FAT/SAT documentation so the next tech knows what's forced.
The CPU handles 244 bytes each of inputs and outputs. It has one integrated PROFINET interface and supports routing. MPI is not available on this variant — if your legacy network relies on MPI, this isn't the drop-in replacement. RS 485 is present, and the CPU can act as both a PROFINET client and server. The client function requires loadable FBs or a CP — not native out of the box.
Width 80 mm, height 125 mm, depth 130 mm. Standard S7-300 form factor — mounts on the DIN rail in the same footprint as other 317 CPUs. If you're swapping from a standard 317 to this fail-safe variant, the mechanical fit is identical; no drilling or rail repositioning needed.