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PICList Thread
'[PIC]: logic gate speeds'
2002\02\18@121704 by Ted Mawson

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The maximum clock speed I understand that a PIC can count at is 50 MHz - correct?

I want to count at higher frequencies - up to 500 MHz and I'm looking to use a logic counter to divide 500 by 16 and give an input frequency into the PIC of  500/16 = 31.25 MHz.

There's a 7400 series chip, the 74F161 that divides by 16 but the max i/p frequency is 100 MHz.  Are there any 7400 series other than F that can go faster or any equivalents that y'all know of?

Can anyone point me to a counter, ideally pre-settable and with accessible (to read) outputs, that could take a clock input for counting faster than 100 MHz and divide by 16?

Ted Mawson
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2002\02\18@122316 by Martin Peach

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I think ECL is the logic family you want.
/\/\/\/*=Martin

----- Original Message -----
From: "Ted Mawson" <.....PICmanKILLspamspam@spam@PORTFOLIOPM.COM>
To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Monday, February 18, 2002 12:13 PM
Subject: [PIC]: logic gate speeds


> The maximum clock speed I understand that a PIC can count at is 50 MHz -
correct?
>
> I want to count at higher frequencies - up to 500 MHz and I'm looking to
use a logic counter to divide 500 by 16 and give an input frequency into the
PIC of  500/16 = 31.25 MHz.
>
> There's a 7400 series chip, the 74F161 that divides by 16 but the max i/p
frequency is 100 MHz.  Are there any 7400 series other than F that can go
faster or any equivalents that y'all know of?
>
> Can anyone point me to a counter, ideally pre-settable and with accessible
(to read) outputs, that could take a clock input for counting faster than
100 MHz and divide by 16?
>
> Ted Mawson
> .....PICmanKILLspamspam.....portfoliopm.com
>
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>

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2002\02\18@123743 by Peter Onion

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On 18-Feb-02 Ted Mawson wrote:
> The maximum clock speed I understand that a PIC can count at is 50 MHz -
> correct?
>
> I want to count at higher frequencies - up to 500 MHz and I'm looking to use
> a logic counter to divide 500 by 16 and give an input frequency into the PIC
> of  500/16 = 31.25 MHz.
>
> There's a 7400 series chip, the 74F161 that divides by 16 but the max i/p
> frequency is 100 MHz.  Are there any 7400 series other than F that can go
> faster or any equivalents that y'all know of?
>
> Can anyone point me to a counter, ideally pre-settable and with accessible
> (to read) outputs, that could take a clock input for counting faster than 100
> MHz and divide by 16?


Google search for "VHF  Prescaler" found me at
http://www.qsl.net/om3cph/vhf_uhf.html

which has a 1.3Ghz freq counter based on 16F84

Maybe you could try google next time for yourself ?

Peter

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2002\02\18@123953 by Spehro Pefhany

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At 12:13 PM 2/18/02 -0500, you wrote:


>Can anyone point me to a counter, ideally pre-settable and with accessible
>(to read) outputs, that could take a clock input for counting faster than
>100 MHz and divide by 16?

If you just want a prescaler, have a look at NEC's MMIC prescaler
offerings. They will work down as far as 100MHz or so, and up into the
GHz.

If you need outputs, have a look at OnSemi's various ECL offerings.
More expensive (you can get them from Newark) and you may have level
translation issues.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\02\18@131009 by Ted Mawson

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Peter,

I've done extensive prior searches on Google.  Google is my standard search
engine, it's in my favorites and is number 1 on my links bar; I'm not
someone who asks on this list before doing my own research if that was your
concern?

The Frequency counter you pointed to uses a prescaler which works OK but
means you lose the lowest 8 bits of binary resolution = 2560 kHz steps in
counting on /256 at a gate time of 0.1 secs.

Spehro and Martin's suggestions to search for 'ECL' yeilded (on Google) the
On-Semi device MC10E016 that counts at 700 MHz min and 900 Typical : )  This
also has Q outputs that can be read after the count has happened.

Thanks to all for your input.

Ted Mawson

{Original Message removed}

2002\02\19@053932 by Vasile Surducan

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On Mon, 18 Feb 2002, Peter Onion wrote:

{Quote hidden}

 why Peter ? If he done this I will never found this interested link...

 thanks, Vasile

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2002\02\19@072242 by Peter Onion

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On 18-Feb-02 Ted Mawson wrote:
> Peter,
>
> I've done extensive prior searches on Google.  Google is my standard search
> engine, it's in my favorites and is number 1 on my links bar; I'm not
> someone who asks on this list before doing my own research if that was your
> concern?

So next time say that you have done a WEB search, then we will know where you
are at already....

Your initial post spoke only of 74F161 which made it appear that you had looked
no further than the TTL data book on your shelf !


> The Frequency counter you pointed to uses a prescaler which works OK but
> means you lose the lowest 8 bits of binary resolution = 2560 kHz steps in
> counting on /256 at a gate time of 0.1 secs.


I think you are out by a factor of 1000 !

In a 0.1s count period the bit 0 of the counter equates to 10Hz, so bit 7
equates to 2560 Hertz not KILO Hertz.

Peter

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2002\02\19@121223 by Ted Mawson

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Summary of info I gleaned from this thread...

PIC16F84 chips are good up to a max clock speed of 50-60 MHz (counting on
the RA4 schmitt trigger input)
74HCxx chips are good up to a max clock speed of 36 MHz
74Fxx chips are good up to a maximum of 100-125 MHz
ECL (emitter coupled logic) can get up to 2 GHz

As Peter onion pointed out, I made a simmple error in that a 0.1s count
period the bit 0 of the counter equates to 10Hz, so bit 7 equates to 2560
Hertz not KILO Hertz.

Thanks to all.

Ted Mawson
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