Abstract: In a microcomputer integrated circuit the option of selecting between an RC oscillator or a crystal oscillator for generating the clock for the microprocessor is made available. By making the selection during the manufacturing process, external pin outs and chip area are minimized.

Abstract: In an ultrasonic system for detecting and distinguishing between superimposed and single sheets moving along a transport path, the frequency of the ultrasonic source is kept tuned to the natural frequency of the total system so that the phase displacement detected when a sheet-like object is present between the source and the ultrasonic receiver represents characteristics of the object itself. When no sheet-like object is present the receiver and the source are connected in a feedback circuit producing a certain natural frequency comparable to that which occurs with proximities between a microphone and a loud speaker, and the frequency of an oscillator is tuned to this natural frequency. When a sheet-like object is present the tuned oscillator frequency is applied to the ultrasonic source and its phase is compared with the phase of the ultrasonic signal at the receiver.