The ISO7021 uses an edge based encoding scheme to transfer an input signal change across the isolation barrier versus sending across the DC state. The built in refresh function consistently validates that the DC output state of each isolator channel matches the DC input state. An internal watchdog timer monitors for activity on the individual inputs and transmits the logic state when there is no input signal transition for more than 100µs. This design verifies that the input and output state of the isolator always match.