CPU 317F-2 DP — what this SFB unit brings
The 6ES7317-6FF04-0AB0 is a Siemens fail-safe CPU from the S7-300 family, type SFB (Safety Fault-Proof Basic). It runs the standard S7-300 form factor — 40 mm wide, 125 mm tall, 130 mm deep — and supports a full programming language set: LAD, FBD, STL, SCL, GRAPH, HiGraph, and CFC. That means any S7-300 project already written in these languages ports over without rewriting logic blocks. Key spec: FM 8 — that's the number of fail-safe digital inputs (or the safety-related function modules) the CPU handles internally. For a safety application, FM 8 means you can wire eight safety-rated sensors directly without an expansion module, though the CPU itself is not expandable — so plan your I/O count at order time.
Integration constraints
This CPU does not support PROFIsafe — the safety protocol over PROFIBUS is absent here, so safety communication must be handled via hardwired F-DI/F-DO or a separate safety bus coupler. MPI is also not available; PROFIBUS DP is the onboard fieldbus. For Ethernet connectivity, you need a CP (communication processor): up to 4 CPs via the backplane, and up to 10 CPs on the LAN side total. PtP connections are limited to 8 via CP. The CPU supports PROFIBUS DP routing (only with an active interface) and can act as a DP client via CP and loadable FB, or as a DP server. The GSD file for PROFIBUS integration is available from Siemens' website. Retentive data must be restarted at each restart — plan your startup logic accordingly.