Hardware interview practice
Contain unknowns before scan compaction
During a scan-capture test, one known nondeterministic source can drive X into a response bit before many scan chains feed a compacting signature register. Which DFT measure directly prevents that source from contaminating the compacted signature while preserving other known response bits?
Choose one
Answer choices
- A. Increase the number of shift clocks so the X value eventually becomes a known zero.
- B. Mask the final multiple-input signature register (MISR) bit after compaction while leaving the X source connected.
- C. Force every scan response bit to zero, including all deterministic bits, before compaction.
- D. Apply an automatic test pattern generation (ATPG)-controlled X-mask to the affected response bit before it enters the compactor.