CPU identity and programming scope
The Siemens 6ES7318-3EL01-0AB0 is an S7-300 SFB (Safety Fault-tolerant) CPU with FM 8 — that's 8 function modules integrated, not a slot count. It supports CFC, FBD, LAD, SCL, STL, GRAPH, and HiGraph® for programming, so you can mix IEC 61131-3 languages and continuous-function-chart blocks in the same project.
PROFINET and communication
Integrated PROFINET interface handles IRT (isochronous real-time) for motion or high-speed I/O synchronization, plus standard TCP/IP and UDP via loadable function blocks. No MPI or DPV1 on this CPU — the PROFINET port is your primary fieldbus. It can act as both PROFINET client and server, so it fits as a controller or an intelligent device in a distributed topology. RS 485 is present for point-to-point or simple network connections. For additional CPs (communication processors), the CPU supports up to 4 CPs for LAN, 10 for LAN via CP, and 8 for PtP — enough for a multi-protocol gateway setup.
I/O capacity and diagnostics
Process image handles 244 bytes each for inputs and outputs — that's about 1950 digital points or a mix of analog channels. Forcing is supported, useful during commissioning to override outputs without changing the program. Routing is enabled, so you can access the CPU's diagnostic buffer and program from a remote PG/PC via the PROFINET backbone. Retentive data must be restarted at each restart — it does not survive a power cycle unless you explicitly save it via SFCs. I2t rating is 1.2 A²·s, which matters for fuse coordination on the backplane supply.
Environmental and physical fit
Rated for 0 °C to 60 °C operating ambient — no extended temperature range here, so keep it inside a ventilated enclosure. Dimensions are 120 mm wide, 125 mm high, 130 mm deep; it occupies a standard S7-300 slot width. STEP 7 V5.5 or higher is required for engineering; the GSD file for PROFIBUS is available from Siemens.