All the totally self checking (TSC) circuits known so far [3]-[8] restrict their fault sets to either single or multiple but unidirectional stuck-at faults. Meyer and Sundstrom [20] have considered on line diagnosis of unrestricted faults but the class of circuits proposed by them does not fall under the category of TSC circuits. This paper proposes a new type of circuit model which is TSC for a fault set, consisting of all possible, i.e., unrestricted stuck-at faults on all the gate input and output signal lines. The model uses redundancy in both space and time domains and realizes combinatorial functions. Some important properties of the model are brought out by a set of lemmas and theorems. The viability of the model is demonstrated by a circuit example which uses CMOS technology.

This correspondence suggests a new method of perporming binary multiplication using the quarter square technique. As compared to the previous methods [1],[2] the proposed scheme is more general in that it can be readily applied to numbers of any word length. Moreover, it has been shown that for the eight-bit case the present method is faster, more systematic, and economical than the earlier schemes.

This paper suggests a new method for minimizing the width or bit dimension of control store words in microprogrammed digital computers. It is shown that any given problem can be formulated within the framework of linear programming and that there exists a lower limit CLB to the number of bits. The optimal grouping of subcommands which gives this minimal width is also readily obtainable.

This correspondence points out that the usual terminal correction for nonrestoring division can always be made in such a way as to permit concatenation of the primary and secondary quotients to form a double precision answer. This eliminates the necessity of any separate postcorrection as suggested in [1] and [2].

A decomposition and reconstruction approach for synthesizing an arbitrary Boolean function with a minimum number of threshold logic elements connected by feedforward paths only is presented. Attention is mainly focused on cascade-type realizations. The approach has the advantage that near-minimal solutions are readily derived. An estimate of how closely the minimality has been approached is obtainable in this method. The method has been successfully applied by the authors to Boolean functions of 5 and 6 variables.