TOTALLY SELF-CHECKING CHECKERS WITH SEPARATE INTERNAL FAULT INDICATION

The design of a novel class of totally self-checking (TSC) checkers with two separate output indications EN and FN is described. FN is independent of input errors and indicates internal faults only. On the other hand, the output EN indicates input errors as well as a small number of internal faults. This design technique, while improving the maintainability of the TSC networks that locate the fault in the functional circuit or in the checker itself, also increases the correct response probability of the error indication output EN. The TSC checkers presented utilize redundant copies of a given normal TSC checker which are monitored by a TSC reduction circuit operating like a TSC vote taker. The TSC reduction circuits can be easily designed using an algebraic approach based on a two-element Boolean algebra with a more efficient set of self-checking operator blocks.