Technical Report CS0073

Title: A Practical Approach to Fault Detection in Combinational Networks
Authors: Adi Tzidon, Israel Berqer, MichaeI Yoeli
Abstract: In this paper the advantages of exhaustive testing of combinational networks are investigated. The method consists of applying all possible input combinations and checking only some attributes of the output vector. It is shown that by abandoning the requirement of minimal testing time (practically insignificant for medium-sized networks) a substantial reduction of testing data to be stored is obtained, and the generation process is simplified. It is shown that

a} In tree networks the detection of any multiple stuck-at fault is accomplished by checking the parity of the number of ones in the truth vector (odd -for any faultless tree network; even -whenever at least one stuck-at fault occurred.) Generation stage is superfluous. b} Any single stuck-at fault in any network realizing an unate function affects the number of ones in the truth vector. Thus the generation stage consists of computing the said number and the detection stage of checking this number by counting.

c} For general functions realized by networks without internal fanout a further function-dependent classification is made and methods of selecting suitable attributes for fault detection are described. At most 2n bits of testing info~mation are necessary to perform single stuck-at faults detection for functions of n variables.

Basic structure of testing device and efficient algorithm to compute the number of ones for a given expression are also presented.

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