Abstract: A one out of N checking circuit for determining whether exactly one of N signal lines is active at any given time. The circuit includes a hierarchal structure of nodes which pairs the N signal lines together in a series of steps. Each node includes a par of output signal lines. The first signal line carries a signal representing whether an active signal line was "seen." The second signal line carries a signal representing whether an error has occurred, i.e. multiple active lines were seen. After each step, the number of signal lines is reduced by one-half until only two signal lines remain. At that point the two signal lines are compared and a final error signal is transmitted.

Abstract: An apparatus for testing cables, cable connections associated with devices and devices in a daisy chain configuration. Cable malfunctions and cable connection malfunctions can be isolated down to a single device in a daisy chain system by looping back the data bus to the control bus or vice versa. A signal is then sent out on the first bus and received back on the second bus. If a cable malfunction is present, the signal received will not be the same as the signal transmitted.