Abstract: An adapter for a multiple operating mode monitor automatically controls the horizontal and vertical deflection circuits of the monitor cathode ray tube depending upon the characteristics of the video source to which the monitor is connected. The adapter has a digital memory for storing sets of monitor operating parameters for each of a plurality of predetermined operating modes at selectively addressable locations. A processor evaluates horizontal and vertical synchronizing signals from a video source to which the monitor is connected to identify one of the plurality of predetermined operating modes corresponding to the synchronizing signals. The operating mode may be evaluated and identified by measuring the period of the horizontal and vertical synchronizing signals form the video source.