Patent ID: 6145105
Filing Date: 2000-11-07
Classification: G01R

Abstract:
A method for use in testing digital systems having a plurality of scannable memory elements and a logic network, each said memory element having a clock input for receiving a common clock signal and being operable in normal mode at a system clock rate, an output and a data input, each said memory element being configurable in a SCAN mode in which said data input of each said element is connected to the output of another of said elements so as to define a scan chain for serially shifting data into and out of said elements, in a HOLD mode for holding data therein during one or more clock cycles of said clock signal, and in a CAPTURE mode in which said input is connected to said logic network, said logic network defining at least one signal path there through for each said elements, said paths extending from the output of said memory elements to the data input of another memory element, at least one of said elements having a signal path duration which is greater than one period of said system clock rate, said method comprising:configuring said elements in SCAN mode:shifting a test stimulus pattern into said scan chain and into said elements thereof while clocking said memory elements at a test clock rate until the test stimulus pattern is shifted into all said scannable memory elements;during said shifting, configuring in said HOLD mode, for a predetermined number of clock cycles prior to a CAPTURE operation, each element having a signal path whose duration is greater than one clock cycle, said predetermined number of clock cycles being equal to or greater than the number of cycles required for a signal output from said each element to propagate to the input of said another memory element;configuring said scannable memory elements in a CAPTURE mode to capture the signal at the inputs of said elements, said signal being representative of the response of said logic network to said test stimulus pattern;configuring said elements in SCAN mode; andshifting out the data from said elements.