Abstract: This invention addresses the testing and diagnosis of failures in the post-logic of products having embedded arrays. The post-logic is the combinational logic that is fed by the embedded array. Since there is no direct access to the post-logic (no direct controllability) it requires special handling. The testing method comprises initializing the array to random values; choosing an address from the array; reading out the information from that address, while applying random signals at the primary inputs. This process is continued for a predetermined number of cycles, while holding that address and applying different random signals at the primary inputs. The process is then repeated while choosing different addresses from the array. Fault diagnosis is accomplished by means of a notebook that retains the past history of the addresses chosen from the array.

Abstract: Delays in critical signal paths are eliminated in circuits employing level sensitive scan design methods for implementing self-test operations. In particular, scan strings associataed with primary input lines are segregated and supplied to a separate distinct signature register so as to permit simplified degating circuitry on the input side of those shift register latches which are in fact associated with primary input signal lines.

Abstract: Phase enhancement means are employed in conjunction with linear feedback shift registers to generate sequences of binary pattern vectors which are much more structurally independent of one another thus enabling more thorough and comprehensive testing of integrated circuit systems. More particularly, the present invention employs a plurality of exclusive-OR gates in an array of one gate per register output cell to generate the desired uncorrelated pattern strings. This facilitates testing of integrated circuit devices and systems and is particularly useful for built-in test situations for very large scale integrated circuits which employ pseudorandom test methods.

Abstract: The LSSD scan paths on a number of logic circuit chips are modified and connected together in series to simultaneously serve as a random signal generator and data compression circuit to perform random stimuli signature generation.