a multiplexing bus controller with input conditioning is provided in which the need for a dedicated microprocessor for handling input filtering , input change detection and serial - to - parallel / parallel - to - serial i / o data conversion is eliminated . the controller is realized in a gate array and provides input data oversampling and output refreshing to eliminate random noise coupled to the data lines . in addition , the oversampled data is filtered to debounce the signal received from the input devices . the input data is converted from serial - to - parallel and checked to detect any change from the previous input data stream . upon detection of an input change , the host microprocessor is interrupted . when the host microprocessor sends data to the bus controller , the bus controller then converts the data to a serial stream for communication to the appropriate output device . additionally , the bus controller is provided with an internal turnaround circuit to loop back outputs to the inputs for diagnostic purposes . very low gate counts realized in the design of the multiplexing bus controller allow it to be realized on a single chip .