Programmable controller with self testing I/O structure.

摘要

A programmable controller includes a processor unit which connects to one or more I/O units that connect to sensing devices and operating devices on equipment being controlled. When placed in the RUN mode, the processor determines the number of I/O units required to execute the user control program, and during each subsequent I/O scan, the number of connected and operating I/O units is checked to insure proper operation.