CPU selection for safety-integrated lines
The Siemens 6ES7315-6FF04-0AB0 is a CPU in the S7-300 family, built around the SFB type with FM 8 function blocks. It supports PROFIsafe, meaning it can run safety-oriented programs directly on the CPU without a separate fail-safe module — a common requirement for machinery guarding and emergency-stop circuits in automated lines. The CPU handles 244 byte inputs and 244 byte outputs, giving it enough I/O bandwidth for medium-scale distributed I/O racks. The process image is adjustable from 10 to 499 bytes, so you can tune the scan to match the fieldbus cycle time rather than carrying unused I/O data.
Programming language support and toolchain
This CPU supports LAD, FBD, STL, SCL, GRAPH, and CFC — covering ladder, function block, structured text, sequential function chart, and continuous function chart. That means the same CPU can serve a relay-logic maintenance team and a CFC-based process control engineer without a hardware swap. Engineering requires STEP 7 V5.2 SP1 or higher with the appropriate HW update. The GSD file for PROFIBUS DP integration is available directly from Siemens, which simplifies commissioning when the CPU is a DP slave on an existing line.
Fieldbus and communication profile
The CPU has an integrated RS 485 interface for PROFIBUS DP, but it does not support MPI or DPV1 natively — DPV1 requires a CP and a loadable FB. For Ethernet-based communication, up to 10 CPs (LAN) and 8 CPs (PtP) can be added via the backplane. Routing is supported only with an active interface, meaning the CPU can forward PROFINET or PROFIBUS telegrams when a CP is present. It can act as both a DP client and server, but the client function needs a CP and a loadable FB — not a native feature.
The module occupies a single S7-300 slot at 40 mm width, 125 mm height, and 130 mm depth. Operating temperature range is 0 °C to 60 °C. The I2t rating is 1 A²·s, which governs the short-circuit withstand of the internal bus — relevant when sizing the backplane power supply and external fusing.
This CPU is not marked as obsolete in the current evidence. If you are maintaining an existing S7-300 line, this CPU is a direct drop-in for the same slot.