The PMC handles the ladder logic (M-codes, safety interlocks, coolant, ATC). The 15M has its own set of "D" (data) and "K" (keep relay) parameters. The Parameter Manual includes the mapping between these and external machine signals.
The Fanuc 15M Parameter Manual dedicates an entire page to safe PWE practices. Fanuc 15m Parameter Manual
Unlike modern Windows-based CNCs with graphic user interfaces, the Fanuc 15M operates on a parameter-driven architecture. Every behavior of the machine—from axis acceleration and spindle orientation to I/O device settings and custom macro security—is governed by numeric parameters stored in CMOS memory. The PMC handles the ladder logic (M-codes, safety
Parameters in the Fanuc 15m are organized into blocks based on their function: How to Enable Parameter Write Enable (PWE) on a Fanuc CNC Fanuc 15m Parameter Manual