Hewlett-packard Company

Bulent I Dervisoglu

Gayvin E Stong

A scannable flip-flop circuit allows data at its data input or its scan input to be stored in the flip-flop at its data output or shifted out of the flip-flop at its scan output. The flip-flop provides control circuitry for selecting the source of the input data and scan data. Data stored at the flip-flop data output may also be shifted out at the scan output. During scan operations, additional control circuitry allows data stored at the data outputs to be preserved.

Flip-flop circuit with controllable copying between slave and scan

A scan-register having first and second data input ports (SYS.sub.-- DATA, SCAN.sub.-- IN), a data output port, and inputs for at least first, second, third, and fourth control signals (SYS.sub.-- CLK, M.sub.-- LOAD, CLK.sub.-- B, CLK.sub.-- A). The scan-register comprises the following elements: first means (12A) having inputs coupled to the first and second data input ports for selectively storing data appearing on one of the said data input ports in accordance with the occurrence of a predefined combination of states of at least the first and second control signals; second menas (10A) having at least one input coupled to the second data input port for selectively storing data appearing on the second data input port in accordance with the occurrence of a predefined state of at least the third control signal; and third means (12B) having at least one input port coupled to an output of one of the first and second means, and further having an output coupled to the data output port, for selectively storing data stored in either the first or second means in accordance with the occurrence of a predefined state of at least the fourth control signal and providing the data stored therein to the data output port.

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Framingham, MA, United States of America

Bulent I Dervisoglu