A Computer Interface for Efficient Zero-Crossing Interval Measurement

A technique is described which makes use of a hardware computer interface to efficiently extract zero-crossing interval information from continuous time signals. Each zero-crossing of the input waveform causes the contents of a clock register to be transferred into a clock buffer register simultaneously with the generation of a computer interrupt. Following this, the clock register is restarted and further zero-crossings are prohibited from affecting the device for a set length of time. This length of time is preset to disallow the interruption of the computer until the present zero-crossing interval can be processed. The interrupted computer may read the clock buffer register which represents the elapsed time between the previous two zero-crossings. Since this method results in the measurement of zero-crossing interval information with a minimum computer involvement, a given computer can spend a maximum amount of time processing zero-crossing interval data. An implementation of the technique for use with a PDP-8/L computer is discussed.