An intelligent programmable process control system is responsive to the states of sensors located along a process for controlling the states of controllable devices located along the process. The system includes a microprocessor which sequentially scans an addressable memory to execute a sequence of...http://www.google.de/patents/US4215397?utm_source=gb-gplus-sharePatent US4215397 - Automatic end-of-scan control system for a programmable process controller with expandable memory
