Abstract: An industrial control system includes an industrial controller and a programming interface. The industrial controller maintains a control program for interfacing with a controlled process. The programming interface is operable to communicate a transaction to the industrial controller. The transaction includes a plurality of operations for modifying the control program followed by a commit transaction command. The industrial controller is operable to preprocess the plurality of operations, designate the plurality of operations with a pending status, and commit the operations and clear the pending status responsive to receiving the commit transaction command.

Abstract: A multitasking industrial controller for real-time control of machinery and the like permits the use of both periodic and event driven tasks by establishing a hierarchy of both task types in the form of priorities that resolve conflicts between events of the same and different types. The unpredictability of the event driven tasks on scheduling of tasks is addressed by watchdog time values assigned to each task which confirm timely execution of the task in practice despite the risk of preemption by other tasks. Flexible software definition of event driven tasks is made possible by delegating the detection of the events to input/output modules executing independently of the processor executing the operating system.