VLSI design for fault-dictionary based testability

The fault-dictionary approach to isolating failures in digital circuits provides inferior isolation accuracy compared to that which is now generally attained with other isolation methods. This limitation is particularly apparent when circuits which use bidirectional bus configurations are being tested. For this reason, fault-dictionary-based isolation has serious economic implications when testing digital circuits which use expensive VLSI or HSIC devices. However, by incorporating relatively minor circuit additions into the design of VLSI and HSIC devices, the normal set/scan or equivalent testability pins can additionally serve to improve actual fault-isolation accuracy. The described additions for improving fault-dictionary-based fault isolation require little semiconductor area, and one configuration even serves to prevent bus-drive conflicts