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'Frequency counter [OT] (A little)'
2000\03\17@085909 by Andrew Kelley

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Does anyone know if one can make Peter Cousens Frequency Counter count
over 50.000 MHz?

Would 10:1 prescaler work?

I think it would but I'm not sure.

It would be more useful that way.

Thanks,
Andrew
Amateur Radio Call: N1YEW
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2000\03\17@093624 by Michael Rigby-Jones

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part 0 4166 bytes
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">I'm sure there was a discussion on these cute frequency counters a while back, and the conclusion was that the 16F84 was not suitable for use with frequencies as high as the old 16C5x devices.&nbsp; A quick look at the very confusing datasheet shows that with the pre-scaler enabled, the minimum high time on T0CKI is 30ns and minimum low time is 20ns.&nbsp; Ignoring rise/fall times that gives a minimum period of 50ns which equates to 20 MHz.</FONT></P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">The 16C54 gives minimum high/low times of 10ns, giving a period of 20ns and a max frequency of 50MHz which is what is claimed in the original design.&nbsp; Porting the code to the 16F84 has effectively reduced the maximum frequency the device can accurately measure.</FONT></P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">The frequency range could be extended via an external pre-scaler fairly easily, but you'll be needing to use some fairly high speed logic to get to 200MHz and employ the correct contrustional techniques for high-speed design.&nbsp; You may also want to modify the PIC code to put the decimal place in the correct location.</FONT></P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Regards</FONT>
</P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Mike</FONT>
</P>
<UL>
<P><FONT SIZE=1 FACE="Arial">{Original Message removed}

2000\03\17@112313 by Dan Michaels

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Mike wrote:
>
>I'm sure there was a discussion on these cute frequency counters a while
>back, and the conclusion was that the 16F84 was not suitable for use with
>frequencies as high as the old 16C5x devices.  A quick look at the very
>confusing datasheet shows that with the pre-scaler enabled, the minimum high
>time on T0CKI is 30ns and minimum low time is 20ns.  Ignoring rise/fall
>times that gives a minimum period of 50ns which equates to 20 MHz.
>
>The 16C54 gives minimum high/low times of 10ns, giving a period of 20ns and
>a max frequency of 50MHz which is what is claimed in the original design.
>Porting the code to the 16F84 has effectively reduced the maximum frequency
>the device can accurately measure.
>

If you take a look at the T0CK1 specs for the 16C6x/7x, you'll find
they are the same as the old 16C54 parts. So you can develop on the '84,
and run (fast) on the '6x/'7x.
==================

{Quote hidden}

I've done this using the 16C73/76 parts and Timer 1, which is 16-bit.
With a 74AC04, for input buffering, feeding into a 74AC74, for divide/4,
it will easily count to > 120 Mhz, and give you a direct 16-bit result.
No 8-bit + (what's that) prescaler (value?) games. This scheme may go
faster than 120, but I never had a faster signal to stick in.

As Mike indicated, you do have to play some games to be sure there
isn't too much ringing at the front end.

regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================

2000\03\17@115001 by jamesnewton

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Drop in a SX 18 and adjust the timing

http://www.scenix.com

http://techref.massmind.org/scenix

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{Original Message removed}

2000\03\17@225853 by Russell McMahon

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An external prescaler would allow this - you would have to modify the "clock
out the balance of the count in the prescaler" part of the code to
accommodate this addition and change any code which processed the results
accordingly.


     Russell McMahon
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{Original Message removed}

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