Program protection module for programmable controller
AssigneeAllen-Bradley Company, Inc.
InventorsWalter V. Casto, Lawrence W. DeLong, Theodore J. Markley, Odo J. Struger
Life of this patent
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Abstract
A program protection module for a programmable controller checks the critical, or protected, portion of the control program each time the controller is switched to the run mode. This is accomplished by reading each control program instruction out of the controller memory and comparing it with a corresponding control instruction stored in a nonaccessible read-only memory. If all the compared control instructions are identical, the module sets a status bit in the programmable controller which enables the protected portion of the control program to be executed. If identity is not found, an alarm is generated and the protected program is not executed.
Claims9
In a programmable controller having a memory which stores a control program, a processor which operates in a run mode to read out the control program instructions and execute them, and I/O interface means coupled to said memory and said processor for connecting the programmable controller to sensing devices and operating devices on a machine to be controlled, the improvement therein of a program protection module which comprises:
- means for storing a standard control program which comprises a plurality of control program instructions;
- means for reading control program instructions from said programmable controller memory and from said standard control program storing means;
- means for comparing each control program instruction read from said standard control program storing means with a corresponding control program instruction read from said programmable controller memory;
- means coupled to said comparing means for indicating that a control program instruction read from said programmable controller memory is not identical to its corresponding control program instruction read from said standard control program storing means;
- and
- a status register coupled to said comparing means for storing a status bit which indicates that all control program instructions in said standard control program storing means are identical to their corresponding control program instructions in said programmable controller memory.
A program protection module for a programmable controller having a memory which stores a control program, a processor which sequentially reads out the control program instructions from the memory and executes them, and I/O interface means coupled to said memory and said processor for coupling status data from a plurality of sensing devices to said programmable controller and for coupling status data from said programmable controller to a plurality of operating devices, said program protection module comprising:
- a read-only memory which stores a standard control program;
- means for sequentially reading control program instructions from said controller memory;
- means for sequentially reading standard control program instructions from said read-only memory;
- means for comparing each control program instruction read from said controller memory with a corresponding standard control program instruction read from said read-only memory;
- and
- means associated with said comparing means for indicating that the control program is not identical to the standard control program.
Dependencies are inferred from the claim text.