Easily testable PLA-based finite state machines

An outline is presented of a synthesis procedure that, beginning from a state transition graph (STG) description of a sequential machine, produces an optimized easily testable programmable logic array (PLA) based logic implementation. Previous approaches to synthesizing easily testable sequential machines have concentrated on the stuck-at-fault model; for PLAs, an extended fault model called the crosspoint fault model has been used. The authors propose a procedure of constrained state assignment and logic optimization which guarantees testability for all combinationally irredundant crosspoint faults in a PLA-based finite-state machine. No direct access to the flip-flops is required. The test sequences to detect these faults can be obtained using combinational test generation techniques alone. This procedure thus represents an alternative to a scan design methodology. Results are presented which show that the area/performance penalties in return for easy testability are small