Designs for self checking flip-flops

The authors introduce two low-cost, modular, totally self checking (TSC), edge triggered and error propagating (code disjoint) flip-flops: one, a D flip-flop used in TSC and strongly fault secure (SFS) synchronous circuits with two-rail codes, the other a T flip-flop, used in a similar way as the D flip-flop but retaining the error as an indicator until the next presetting, to aid error propagation. Thus, the self checking T flip-flop can be used as an error indicator. The self checking D flip-flop is smaller than the duplicate D flip-flop circuitry by 30%. The self checking T flip-flop error indicator is 60% smaller than the pervious error indicator in the literature. These circuits, unlike previously reported circuits, can also detect stuck-at faults in the clock inputs. The authors have also presented TSC/error propagating applications for the above flip-flops: a counter and a shift register