Design for Testability45To observe an input of the AND gate atdrequires setting the other input to 1;therefore, the combinational and sequential observability measures for both inputsaandbare:COa=COd+CC1b+1SOa=SOd+SC1bCOb=COd+CC1a+1SOb=SOd+SC1aIt is important to note that controllability and observability measures calculatedusing SCOAP are heuristics and only approximate the actual testability of a logiccircuit. When scan design is used, testability analysis can assume that all scancells are directly controllable and observable. It was also shown in [Agrawal 1982]that SCOAP may overestimate testability measures for circuits containing manyreconvergent fanouts; however, by being able to perform testability analysis inO(n) computational complexity fornsignals in a circuit, SCOAP provides a quickestimate of the circuit’s testability that can be used to guide testability enhancementand test generation.
This is the end of the preview.
access the rest of the document.
Automatic test pattern generation, SCOAP, testability analysis, testability measures