Hello Sarah Nagata,

The below web site gives assembly example of how to set up the timers for a 89C2051 to measure frequency in hex format. It should be simple to convert that (hex) to ASCII for your VFD display. This example can measure frequency's up 500 kHz. With your faster IC (Philips 89C664) you should be able to beat that.

http://www.e-insite.net/ednmag/in...76&stt=001

Good luck,

Charles Bannister