The present invention operates by verifying correct latch operation in a digital circuit. After a value has been stored in a latch, electronic circuitry can verify that the value has been stored correctly. The electronic circuitry that performs this verification can be tested to insure that it is operating...http://www.google.de/patents/US5130575?utm_source=gb-gplus-sharePatent US5130575 - Testable latch self checker
