Clock system with internal monitor circuitry for secure testing

Details Clock system with internal monitor circuitry for secure testing Clock system with internal monitor circuitry for secure testing

1995-08-30

1997-05-27

Wambach, Margaret Rose

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Clock or pulse waveform generating

327 20, 327294, H03K 519

Patent

active

056336098

ABSTRACT:
A clock system includes internal monitor circuitry such that the clock system is testable in a secure environment. In particular, the clock system includes a plurality of separately enableable clock generator circuit modules. Each of the clock generator circuit modules generates a separate clock signal when enabled. Combining circuitry receives the separate clock signals from those clock generator circuit modules which are enabled and derives a derived clock signal therefrom. Monitor circuitry receives the derived clock signal, detects whether there are transitions in the derived clock signal, and provides a monitor indication of a result of the detection. Thus, the clock system can be tested without providing the separate clock signals outside the clock system. Preferably, the clock system also includes a programmable clock control register that holds clock control data, the clock control data determining which of the clock generator circuit modules are enabled. A processor is connected to program the clock control data in the clock control register circuitry. The processor executes a program that programs the clock control data to enable and then disable each of the clock generator circuit modules one at a time and to query the monitor indication while each of the clock generator circuit modules is enabled.

REFERENCES:
patent: 5406132 (1995-04-01), Housako

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