Mitigating Observability Loss of Toggle-Based X-Masking via Scan Chain Partitioning

Sae Eun Kim, Jaeyong Chung, Joon Sung Yang

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


The Toggle-based X-masking method requires a single toggle at a given cycle, there is a chance that non-X values are also masked. Hence, the non-X value over-masking problem may cause a fault coverage degradation. In this paper, a scan chain partitioning scheme is described to alleviate non-X bit over-masking problem arising from Toggle-based X-Masking method. The scan chain partitioning method finds a scan chain combination that gives the least toggling conflicts. The experimental results show that the amount of over-masked bits is significantly reduced, and it is further reduced when the proposed method is incorporated with X-canceling method. However, as the number of scan chain partitions increases, the control data for decoder increases. To reduce a control data overhead, this paper exploits a Huffman coding based data compression. Assuming two partitions, the size of control bits is even smaller than the conventional X-toggling method that uses only one decoder. In addition, selection rules of X-bits delivered to X-Canceling MISR are also proposed. With the selection rules, a significant test time increase can be prevented.

Original languageEnglish
Pages (from-to)1184-1192
Number of pages9
JournalIEEE Transactions on Computers
Issue number8
Publication statusPublished - 2018 Aug 1

Bibliographical note

Publisher Copyright:
© 1968-2012 IEEE.

All Science Journal Classification (ASJC) codes

  • Software
  • Theoretical Computer Science
  • Hardware and Architecture
  • Computational Theory and Mathematics


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