Checking sequential logic circuits

摘要

A sequential logic circuit includes means for checking, while the circuit is in operation, that it is stepping correctly from one state to the next. The current state of the circuit is encoded as X0-X3. That encoded value is compared with a predicted value Y0-Y3 derived in response to the previous state of the circuit itself and those signals that cause the transition from the previous to the current state. If the two do not match the circuit has not stepped to the correct state. Reduction in hardware is achieved by allowing certain states to share the same encoded value.