Method and apparatus for handling multiplexer contention during

Details Method and apparatus for handling multiplexer contention during Method and apparatus for handling multiplexer contention during

1996-09-27

1998-02-03

Canney, Vincent P.

Excavating

G06F 1100

Patent

active

057152560

ABSTRACT:
A method and apparatus for handling multiplexer contention during scan. During a test scan of a multiplexer circuit, it is possible for multiple inputs of a multiplexer to be selected at the same time in what is referred to as multiplexer contention. If the selected inputs are of different logical values, this contention may result in high power consumption and damage to the circuit. The invention prevents the adverse consequences of multiplexer contention by disabling one direction of the driving capability for each driving gate in the multiplexer during a scan. Thus, the multiplexer output can be driven to only one logical value regardless of the logical values of the selected inputs. A controllable impedance element, such as a transistor, is coupled between an input driving gate of a multiplexer circuit and a voltage supply node. The impedance element is responsive to a scan control signal, such that the impedance element is disabled, i.e., at high impedance, during a scan procedure. The input driving gate is therefore prevented from driving the multiplexer output towards the potential of the voltage supply node during a scan procedure. During normal operation, the impedance element is enabled, i.e., at low impedance, and the input driving gate is substantially unaffected.

REFERENCES:
patent: 5631911 (1997-05-01), Whetsel, Jr.
patent: 5631912 (1997-05-01), More, Jr.

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