Analog to digital conversion using the IRQ interrupt of the Apple II

Abstract

A simple analog to digital conversion system is presented that allows one to capture an analog input signal, store it on a memory page of the Apple IIs RAM and if desired reconstruct this disturbance in voltage vs. time progression on high resolution graphics or on print. The conversion peripheral makes use of 8-bit ADC 0809 interfaced into the Apple via the John Bell Interface Card. The software developed uses the IRQ input of the 6502 in servicing the ADC Facility. Electrical noise characteristic in the environment is disregarded thru the incorporation of a trigger subroutine into the software.