Abstract: Digital logic apparatus for synthesizing a phase-modulated carrier wave wherein phase shifts between successive carrier-wave segments encode data elements. Carrier-wave segments having different phases are stored in the form of digitally encoded samples in a memory. A digital-to-analog converter is connected to convert sequentially read samples of selected segments into the phase-modulated carrier wave. A combinational logic circuit selects each segment to be addressed according to an applied data element and the phase of the previously selected segment. Means are provided to overlap and blend successively addressed segments to provide smooth phase transitions in the synthesized wave.

Abstract: Each of the inputs of an analog multiplexer are connected to a plurality of capacitive keyswitches and a reference capacitor. At the first multiplexer scan position, the reference capacitor is charged through a charging resistor and when a predetermined voltage is reached a threshold amplifier is caused to respond. The time period required to charge the reference capacitor is stored and compared with the time period required to charge each of the keyswitches. A control signal is generated in response to this comparison providing a signal representative of the capacitive value of the keyswitch in relation to the reference capacitor and thus the operative condition of the keyswitch.