US Patent 8234420 Method, system, and apparatus for communicating using multiple controllers

Operating a control system includes repeatedly transmitting a first interrupt to at least one interface unit by a first controller of a plurality of controllers, wherein the first interrupt is transmitted at a first frequency. A first response is received at the first controller from the at least one interface unit responsive to the first interrupt, and a second response is received at a second controller of the plurality of controllers from the at least one interface unit, wherein the second response is aperiodic with respect to the first frequency.