You can even make this switching between prescaled and non-prescaled
automatic. Always try the prescaled input first. If you count a frequency
too low to require the prescaler, then switch to the non-prescaled input.
The PIC can do this and can also adjust the number it displays(adding a
scale factor of 100 or whatever your prescaler does) as well as the gate
period (interval over which you count pulses for each reading).

You can buy prescaler chips which are good up to a few GHz for only a few
dollars a piece from Mouser

http://www.mouser.com  I think they are made by NEC and are under the MMIC
(Microwave Modular(?) Integrated Circuit) section.

The only difficult part then is making your PCB layout for the prescaler
adequate. Depending on the amplitude of the signals you intend to measure,
you may be able to get away with just keeping the traces from the connector
to the IC very short, and using surface mount decoupling caps for the IC.

Sean

At 06:22 AM 5/17/01 +0100, you wrote:
>The URL's you provided appear to be offline.
>
>If you have a design for a 40MHz counter then add a "Divide by 100"
>prescaler and 2 inputs, one <40MHz the other >40MHz.
>
>Regards
>Chris Carr
>
>--
>http://www.piclist.com hint: PICList Posts must start with ONE topic:
>[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads