US 5,636,124 AGranted

Multitasking industrial controller

AssigneeAllen-Bradley Company, Inc.

InventorsCharles M. Rischar, David R. Rohn, David A. Johnston, Raymond Husted

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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.

Claims12

Dependent claims

An industrial controller operating controlled equipment according to a control program divided into at least two tasks each having a starting and completion point, the controller comprising:

(a) an I/O module receiving electrical inputs from the controlled equipment;
(b) a control terminal for entering data from the user providing for each task:
a task priority, a task characterization as to whether the task is periodic, and thus to be executed to completion regularly according to a time period, or event triggered, and thus to be executed upon occurrence of an event, the event being a change in a predetermined electrical input;
(c) an electronic memory communicating with the I/O module and the control terminal and storing:
(i) the at least two tasks of the control program;
(ii) a task scheduling table receiving the task priority and task characterization from the user;
(iii) an operating system program;
(d) an electronic processor communicating with the electronic memory and the I/O module to receive the electrical inputs and operate according to the inputs and the control program, and executing the operating system program to:
(i) identify a highest priority periodic task requiring current execution based on the task priority and the time period of the task;
(ii) identify a highest priority event triggered task ready current execution based on the occurrence of its event;
(iii) if there is no ready event triggered task of higher priority than the highest priority periodic task, execute once to completion the highest priority periodic task;
(iv) if there is no highest priority periodic tasks of higher priority than the ready event triggered task execute once to completion the ready event triggered task.

9 more elements

Dependencies are inferred from the claim text.