Automatic end-of-scan control system for a programmable process controller with expandable memory

Claim 1

An intelligent programmable process control system responsive to the states of sensors located along the process for controlling the states of controllable devices located along said process, said system comprising: (a) addressable memory means for storing a sequence of boolean logic instructions for controlling said process; (b) microprocessor means coupled to said memory means for sequentially scanning said memory means to execute said sequence of boolean logic instructions, said microprocessor means including first means for generating an end-of-scan signal upon execution of the last instruction of a sequence contained in said memory means; (c) image register means coupled to said microprocessor means for storing input bits representative of the states of said sensors and output bits representative of the states of said controllable devices as computed by said microprocessor means in accordance with said sequence of boolean logic instructions; (d) receptor means adapted to receive extended addressable memory means, said extended addressable memory means being effective when positioned in said receptor means to store additional instructions of said sequence of boolean logic instructions, said receptor means including means for detecting the presence or absence of said extended addressable memory means in said receptor means and providing an indicator signal indicative thereof, and (e) second means coupled to said receptor means and responsive to said indicator signal for generating an end-of-scan signal whenever said microprocessor means attempts to address said extended memory means and said indicator signal indicates that said receptor does not contain said extended memory means.