Frequency Counting Nascom

by J.A. Hart

This program measures frequency, time is kept track of using register BC. The port is sampled for approx. 2,000,000 T states or 1 second. The number of cycles are counted in the HL register pair. The number of cycles counted is converted to decimal and then displayed giving a counting display.

The program will work at 2 MHz without wait states or 4 MHz without wait states. At 4 MHz location 0CCFH should be ADD HL,HL as the port is only scanned for half a second and the number of cycles counted is only half compared to operation at 2 MHz for the same input frequency. The accuracy is dependent on the Nascom clock oscillator and should be O.K. for tuning UART Serial Clock oscillators.