*** Frequency Counter ***
This is a microprocessor based frequency counter
which was inspired by the integral 50 Mhz prescaler found on
the Microchip PIC series micros.
The basic design permits direct counting to 50 Mhz.
Only 7 readouts are used for two reasons.
First, that exceeds the precision of the simple crystal timebase and
second, that's all that would fit in the box used to package the unit!
An auto-ranging feature in this version relocates the decimal point
to configure the display to show MHz when the input exceeds 10MHz
and returns the point to display KHz when the input is less than 1 MHz.
A power-on-self-test cycles the readouts through all their numbers
just because it was an easy function to add.
Prescalers have been added to the basic design
to extend the range as high as 6GHz with an accompanying minor
modification to the software.
I used some cute but, rather pricey, readouts made by Hewlett Packard
(Later, Agilent, and the readout division may have just recently been sold to another company)
There is enough code space & execution time available in the program
to drive more economical 7 segment style displays if desired
Note that the basic technique can be used to measure frequencies up to 50 Mhz
for purposes other than direct display.