PLC CPU UNIT, SYSTEM PROGRAM FOR PLC, AND STORAGE MEDIUM HAVING SYSTEM PROGRAM FOR PLC STORED THEREIN

摘要

A system program includes a first execution control instruction to start execution of a first control program at every first execution cycle of the same period as a control cycle period, and a second execution control instruction to start execution of a second control program at every second execution cycle whose period is an integer multiple of at least twice the control cycle period. The second execution control instruction includes an instruction to start, in an control cycle in which a second execution cycle starts, execution of the second control program after the end of execution of the first control program, and if the second control program is not completed before the end of the control cycle, to start execution of an unexecuted part of the second control program after the end of execution of the first control program in the next control cycle.