US Patent 7765353 Simple identification of low-level signals between circuit cards

A method and apparatus are provided for conveying low level signals from a first circuit card to a second circuit card. The low level signals are encoded using a simple integer value N, and the low level signals are then communicated to the second circuit card as a sequence of N alternating values. A binary counter is used to generate the sequence of alternating values using the output of a single pin of the counter, although a second pin may be used to generate a clock signal. The invention allows all low level signals to be communicated in a robust yet simple way, minimizing the chance of spurious signals being generated upon hot insertion or extraction without complicated ad hoc solutions.