Hi,

Steve you're right, there is not difference between a prescaler and a divider by 10. But in frequency meter application, there is often a divider by 10 for each digit.
As I'd like to build a 1.3GHz frequency meter with 8 or 9 significant digits (10 or 100Hz accurate), this means a lot of hardware....

Peter, by using a prescaler by 256, the maximum signal to measure is 5078125 Hz so a pulse every 19.7 microseconds. Can't we measure a 20microseconds top ?

Next, the timer accuracy will define the significant bits. With a 16 bits timer and 1.2GHz signal, the accuray is 200KHz.
With a 24 bits timer, the accuracy is 800 Hz
With 26 bits, 200Hz
With 28 bits, 50Hz

With 24 bits, 2^24=16777216 tics, this means the microcontroller should have a clock above 16,7 MHz. Let's take a 24MHz clock and it should works.

What is your filling ?

Regards
Stephane