Fault grading of large digital systems

Cost-effective and accurate fault simulation of very large digital designs on engineering workstations is proposed. The hierarchical approach reduces memory requirements drastically by storing the structure of common repeated subcircuits only once. The approach allows flexible multilevel simulation. The simulation algorithms are at the switch-level so that general MOS digital designs with bidirectional signal flow can be handled, and both stuck-at and transistor faults are treated accurately. The fault simulation algorithms have been implemented as a prototype that was used to determine the fault grade of a model of the Motorola 68000 microprocessor on SUN Microsystems workstations