SIMATIC S7-400, EXM 438-1 I/O extension for FM 458 4x analog outputs 16-bit EXM 438-1 not spare part-compatible for EXM438 Application module of the SIMATIC S7-400 for complex and medium-sized applications. Expandable by local I/O and communication modules and configurable in CFC/SFC with the D7-SYS block library