William H. McAnney

Random pattern testability of delay faults

La detection de chemins lents en logique combinatoire par des structures aleatoires est etudiee

Identification of failing tests with cycling registers

A method is presented of operating on signatures from a cycling register such that the complexity of identifying multiple failing tests is comparable to that of identifying a single failing test. The method has some interesting aliasing characteristics. The authors show the probability of aliasing and suggest how it can be kept relatively small. The efficiency of the method decreases as the number of failing tests increase. The reduction in efficiency is due to an increase in aliasing probability caused by footprints being lost in the cycling registers. The larger the number of failing tests, the greater is the chance that aliasing will occur.<<ETX>>

Built-in test for RAMs

A built-in test structure is described that is based on the ATS algorithmic test sequence, which provides the shortest possible test for stuck-at faults in a random-access memory (RAM). An initialization step has been added to ATS that allows the modified procedure to detect bit-rail faults. In the test mode, the memory address register is converted to a count-by-three circuit controlled by a four-latch test sequencer. A simple data-compare circuit is placed on the RAM outputs to detect faults.<<ETX>>

A multiple seed linear feedback shift register

The authors describe the design of an LSSD-(level-sensitive-scan-design) based LFSR (linear feedback shift register) which is capable of changing seeds by applying a pair of clock pulses at the time of the change. This LFSR is controlled by two separate clocks, one for the normal LFSR operation and one for the change-of-seeds option. The newly generated seeds are uniformly distributed over the entire pattern space. The change of seeds is fast, since it is accomplished by a pair of clock pulses rather than by long scan operations.<<ETX>>

Testing for coupled cells in random-access memories

Two test strategies for memory testing are compared for their ability to detect coupled-cell faults in an n-word-by-1-bit random access memory. In both strategies the data-in line is randomly driven. One of the two strategies uses random selection of both the address lines and the read/write control. The other strategy sequentially cycles through the address space with deterministic setting of the read/write control. The relative merit of the two strategies is measured by the average number of accesses per address needed to meet a standard test quality level. >