Industrial controller with program synchronized updating of back-up controller

摘要

An industrial control system employs a primary and secondary controller each having a processor and an I/O data table. Updating of the secondary processor's I/O data table is accomplished synchronously with execution of the program in the primary processor at a particular point in the program. A tracking of changes in the I/O data table of the primary processor is used to transmit only changes in the I/O table to the secondary processor thereby avoiding undue interruption of the executing program while preserving synchronicity.