Patent ID: 6487688
Filing Date: 2002-11-26
Classification: G01R

Abstract:
In a method of testing a circuit having two or more tri-state bus drivers, each having a data input, an enable input and a data output, said data outputs being connected together to form a bus, said circuit having core logic, a plurality of scannable memory elements, each having a clock input, an input connected to the output of the core logic and/or an output connected to an input to said core logic, and being configurable in scan mode in which said memory elements are connected to define one or more scan chains and in normal mode in which said memory elements are connected to said core logic in normal operational mode, said core logic generating a data input and a functional enable signal for each said tri-state bus drivers, said bus providing input to said core logic, said method including a shift-in sequence for clocking a test stimulus into said memory elements, a capture operation for capturing the response of the core logic to the test stimulus and a shift-out sequence for clocking captured responses out of said elements for analysis, said method comprising the improvement of:storing a driver select code signal in scannable memory elements associated with said bus drivers, said driver select code signal identifying at most only one of said driver which is to be active during normal mode; decoding the output of said associated scannable memory elements and generating a decoded driver select signal for each of said bus drivers; gating each said decoded driver select signal with a functional driver enable signal for each said driver to generate a driver enable signal and applying said driver enable signal to said enable input of said driver; disabling all of said drivers by generating an inactive driver select signal for each said bus drivers when said plurality of memory elements are configured in scan mode; and applying said driver enable signal to each said bus drivers when said plurality of memory elements are configured in normal mode.