METHOD FOR TESTING CIRCUITS WITH TRI-STATE DRIVERS AND CIRCUIT FOR USE THEREWITH

摘要

A scan-testing method a circuit having tri-state bus drivers involves disabling all drivers during scan intervals and enabling at most a selected one of the drivers during the capture interval by generating a driver select signal for each driver and gating each driver select signal with the circuit functional enable signal for each driver to generate a driver enable signal, the driver select signals being generated in such a manner that at most only a selected one of the drivers is active during the capture interval. The selected one of the drivers is selected by loading a driver select code into memory elements during the scan-in sequence and decoding the driver select code to produce the driver select signals. A driver control circuit including the memory elements for storing the driver select code, a decoding circuit for decoding the code and generating driver select signals, and gating circuitry for gating the driver select signals and driver functional enable signals for generating driver enable signals. The driver control circuit is controlled by a control signal which is inactive during scan operations and active during capture operations.