Method and Apparatus for Synthesis of Multimode X-Tolerant Compressor

An apparatus for compressing test response data from a plurality of scan chains and a plurality of shift cycles comprising an input selector coupled to a compactor circuitry wherein groups of the plurality of the scan chains are specified by sets of groups such that:

• (i) the groups disallow sharing a common scan chain from the plurality of scan chains, within a particular set of groups of the sets of groups,
• (ii) a scan chain belongs to at least two different sets of the sets of groups;
• and
• wherein the compactor circuitry selectively receives per shift basis test response from:
• 1) a group of scan chains;
• 2) an intersection of at least two groups of scan chains;
• and 3) an union of at least two groups of scan chains, and
• wherein at least one common scan chain is shared between the groups of the sets of groups, such that the groups of a first set of groups share at least one common scan chain with at least one group of a second set of groups.

A computer readable medium, comprising:

• computer instructions to perform a method of compressing test responses of a circuit under test, the circuit under test including a plurality of scan chains which includes a plurality of known scan chains and a plurality of unknown scan chains, the method comprising:
• dividing a plurality of scan chains in a circuit under test among at least groups of scan chains and sets of groups such that:
• (i) the groups disallow sharing a common scan chain from the plurality of scan chains, within a particular set of the sets of groups,
• (ii) a scan chain belongs to at least two different sets of the sets of groups;
• and
• based on at least said dividing, selectively compressing test response data from the plurality of scan chains over a plurality of shift cycles.