Programmable controller having a system for monitoring the logic conditions at external locations

摘要

A system for monitoring the logic conditions at the external addressable locations of a programmable controller wherein intermediate memory units are provided for controlling separate input and output locations. The controller periodically sequences the data in the intermediate memory units to maintain the logic conditions in the input and output locations. If the logic conditions are to be updated, the controller obtains access to the sequencing arrangement and changes the logic conditions within the intermediate memory units. Thereafter, the sequencing continues to maintain the desired logic conditions in the input and output locations.