Restartable logic bist controller

Abstract

A method and apparatus for testing an integrated circuit using built-in self-test (BIST) techniques is described. In one aspect, a BIST circuit comprises a scan monitor with hold logic and a signature generation element. The hold logic is operable to suspend signature generation in the signature generation element at any desired point in the test sequence. In some embodiments, the hold logic comprises a scan-loadable signature hold flip-flop which allows the logic BIST controller to be restarted from any selected pattern within a pattern range and to run to any subsequent pattern. The BIST session can be run incrementally, testing and reporting intermediate MISR signatures. External automatic testing equipment can suspend signature generation at selected times during a BIST session to prevent tainting of the signature generation element. The hold logic also may comprise a rotating hold ring to suspend signature generation during predetermined shift cycles.