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Unformatted text preview: 10/27/2011 1 ECE 553: TESTING AND TESTABLE DESIGN OF DIGITAL SYSTES Functional testing 10/27/2011 2 Overview Motivation and introduction Structure independent approach Structure dependant approach Organization/architecture dependant approach Microprocessor testing Memory testing Summary 10/27/2011 3 Motivation and Introduction Ref: Abramovici, et. Al Reference book Section 18.2 of the text (for understanding the problem) Motivation Structural information can facilitate testing we show this for combinational and sequential circuits Organization/Architecture information can make testing of microprocessors and memories practical Develop fault models when we are to use this kind of information 10/27/2011 4 Structure independent approach Combinational circuit testing Exhaustive testing of circuits that do not have very large number of inputs Note: if a fault can cause the circuit to behave like a circuit with states (i.e. causes increase in the number of states combinational circuit becomes sequential in nature) then exhaustive testing may not fully test the circuit. Example of such a fault is stuck-open fault in a CMOS implementation 10/27/2011 5 Structure independent approach Combinational circuit testing (contd.) A non-exhaustive functional test must be carefully designed otherwise it may not achieve the desired objective. Consider a 2-to-1 mux. A non-exhaustive functional test is given below: A B S D S A B D 1 x 0 0 0 0 0 0 x x x 1 1 1 1 1 10/27/2011 6 Structure independent approach Combinational circuit testing (contd.) A fully specified test can potentially be (the one that repeats values in the test) as follows: This test can not test stuck-at fault on the control line S A B S D S A B D 1 1 0 0 0 0 0 0 0 1 0 1 1 1 1 1...
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