PROGRAMMABLE CONTROLLER PROCESSOR FOR CONCURRENTLY EXECUTING MULTIPLE USER PROGRAMS

摘要

A programmable controller has a processor with a memory that stores a plurality of user defined control programs for operating machinery and a list of the stored programs in the order of execution. The processor sequentially selects each program from the list and executes the program until a defined point in the program is reached. At that time, execution of the program is suspended and another program is selected from the list. If a ladder logic type program is selected, the processor makes one execution scan through the program before suspending execution. If a sequential function chart program is selected, one section is executed and a transition condition associated with that section is evaluated before suspending execution of the sequential function chart program. Following the suspension of each control program's execution, the processor reads input data and writes data to output devices. The execution list of the stored programs is dynamic in that an executing user defined control program may add or delete a program on the list or inhibit the execution of a program that remains on the list.