Sun Microsystems, Inc.

Srinivas Nori

Marc E Levitt

Sandeep K Aggarwal

Slobodan Simovich

Ramachandra P Kunda

A circuit is disclosed which allows an IN-Test to be performed on an integrated circuit (IC) without having to stop the external clock sources by disabling the IC's internal phase-locked loops. Information indicative of the IC's clock mode and of the desired stop mode is contained within the IC's clock control register. In one embodiment, the internal clocks may be stopped in either of three stop modes while operating in one of three clock modes. When it is desired to stop the IC's internal clocks, the clock control register provides a stop instruction signal STOP.sub.-- INSTR to a clock control circuit which, depending upon the particular stop mode and clock mode encoded in signal STOP.sub.-- INSTR by the clock control register, asserts a enabling signal to a disable clock circuit. In response to this active-high enabling signal, the disable clock circuit asserts a zero feedback signal to the internal phase-locked loops of the IC and thereby forces the voltage controlled oscillators within the phase-locked loops to hold internal clocks low. In this manner, the IC internal clocks may be stopped to allow a test vector to be scanned out of the IC during an IN-Test without stopping the external clock source.

Clock stopping schemes for data buffer

A logic signal validity verifier for use in determining the validity of the logic states of a group of logic signals includes an inactive signal fault monitor for determining when all of the logic signals are in an inactive signal state and an active signal fault monitor for determining when more than one of the logic signals are in an active signal state. Where the logic signals are differential, the logic signal validity verifier further includes a differential signal fault monitor for determining when corresponding pairs of the differential logic signals are in the same active or inactive signal state.

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San Jose, CA, United States of America

Srinivas Nori