Circuitry and method that allows for external control of a data security device (Assignee -- National Semiconductor Corporation)

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2-26-96. MicroPatent:

Circuitry and method that allows for external control of a data security device (Assignee -- National Semiconductor Corporation)

Abstract: A data security device is unitarily formed in an integrated circuit. A processor of the data security device operates in response to a clock signal provided at a clock input of the processor. Clock signal generation circuitry generates an internal clock signal. First processor-readable program code is configured to cause the processor to detect an internal, protectable, non-volatile indication of a state of the integrated circuit data security device. For example, one indication may be that non-volatile memory of the data security device has never been initialized. Another indication may be that the non-volatile memory of the data security device contains a manufacturing test pattern. Clock signal selection circuitry selectively provides a path for either the internal clock signal to be provided to the clock input of the processor or, alternatively, for an externally-provided clock signal to be provided to the clock input of the processor. Second processor-readable program code is configured to cause the processor to control the selection by the clock signal selection circuitry responsive to the state indication.

Ex Claim Text: A data security system unitarily formed in an integrated circuit, comprising: a processor that operates in response to a clock signal provided at a clock input of the processor; clock signal generation circuitry that generates an internal clock signal; first processor-readable program code configured to cause the processor to detect an internal, protectable, non-volatile indication of a state of the integrated circuit data security system; clock signal selection circuitry that selectively provides a path for the internal clock signal to be provided to the clock input of the processor or a path for an externally-provided clock signal to be provided to the clock input of the processor; and second processor-readable program code, responsive to the state indication, configured to cause the processor to control the selection by the clock signal selection circuitry. circuitry.

Assignee: National Semiconductor Corporation

Patent Number: 5604713

Issue Date: 1997 02 18

Inventor(s): Short, Timothy A.Childs, Matthew H.

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