CPU 1518F-4 PN/DP — the failsafe workhorse for demanding lines
The 6ES7518-4FX00-1AB0 is a SIMATIC S7-1500 CPU 1518F-4 PN/DP, the failsafe variant of the 1518 series. It handles both standard and safety logic on one CPU, with PROFIsafe V2.4 / V2.6 support for SIL 3 safety applications up to the process image limits. The process image is 32 kB for inputs and 32 kB for outputs — all I/O data lives in the process image, so no remanent data shuffling for fast logic scans. That matters when you're running a coordinated safety shutdown sequence across multiple remote racks. Operating range is -40°C to 70°C, which puts it in the extended-temperature class for unheated cabinets or outdoor enclosures. If your line sees freeze-thaw cycles or a hot summer afternoon inside a non-climate-controlled panel, this CPU handles it without derating.
Network interfaces and protocol support
The X3 interface supports 1 Gbps, which is the high-speed backplane for PROFINET IO — only possible on the CPU 1518. The X1 and X2 interfaces run at 100 Mbps for standard PROFINET and MRP rings. MRP is supported as both redundancy manager and client, so this CPU can sit at the heart of a media-redundant ring without an external switch. MRPD is also supported, but requires IRT — note that IRT is not listed as supported on this variant, so MRPD may be unavailable in practice. Protocol stack includes TCP/IP, UDP, DHCP, DNS, DCP, LLDP, SNMP, HTTP/HTTPS (standard and user pages), and MODBUS TCP. The RS-485 interface at X4 supports point-to-point serial communication for legacy drives or remote I/O.
Programming languages and safety integration
Supported programming languages include LAD, FBD, STL, SCL, and GRAPH — both standard and failsafe variants for LAD and FBD. That means you can reuse existing safety function blocks from older S7-300/400 F-systems without rewriting them in a different language. Integrated PID controllers are available for temperature and valve positioning, both with integrated optimization. This saves a separate loop controller for simple thermal or flow loops.
Sourcing and lifecycle posture
For a BOM freeze or critical-spare holding, this is the failsafe variant you want in the cabinet before the line goes down. The wide temperature range and PROFIsafe support make it a one-for-one swap for any existing 1518F-4 PN/DP installation.