Nick, can the Attiny25 divide down a 20Mhz input. I understand the 12fxxx pics 
max out at 20Mhz on a input so not sure if they would be suitable for my 
purpose. Can't seem to find anything in the datasheet for the tiny that 
explains the maximum frequency on a input pin.

-=Bryan=-

> Date: Wed, 13 Jan 2016 12:12:39 -0800
> To: [email protected]; [email protected]
> Subject: Re: [time-nuts] Generating a solid PPS from 10Mhz source
> From: [email protected]
> 
> Just shy of a half dozen folks have asked, so I'll post here as soon as I 
> finish cleaning it up. I'll put it on Github when it's ready. I just need a 
> day or two. 
> 
> Sent from my iPhone
> 
> > On Jan 13, 2016, at 6:43 AM, Nick Sayer via time-nuts <[email protected]> 
> > wrote:
> > 
> > If anyone is interested in the equivalent functionality using an ATTiny25 
> > (for instance, if you’re already heavily invested in AVR instead of PIC, 
> > like I am), ping me. I’ve privately written code to solve almost the same 
> > problem and it could easily be adapted into doing the same job.
> > 
> >> On Jan 13, 2016, at 5:23 AM, Edesio Costa e Silva 
> >> <[email protected]> wrote:
> >> 
> >> Hi!
> >> 
> >> Try TVB's picDiv at http://www.leapsecond.com/pic/picdiv.htm
> >> 
> >> Edésio
> >> 
> >>> On Wed, Jan 13, 2016 at 09:22:09AM +0000, Jerome Blaha wrote:
> >>> Hey Guys,
> >>> 
> >>> Is there an easy circuit to build that can consistently deliver a 1 PPS 
> >>> from a 10MHz source with excellent resolution and repeatability?  My 
> >>> first application is to test different 10MHz oscillators without a TIC 
> >>> always attached and then compare the PPS output change over time against 
> >>> a master GPSDO PPS with an HP53132A.
> >>> 
> >>> The circuit used for PPS generation would have to deliver consistent PPS 
> >>> output with preferably not more than 100ps noise or jitter, assuming a 
> >>> perfect source.  I'm totally guessing that for this resolution, the PPS 
> >>> would have to be generated and accurate to within 0.001Hz every second.  
> >>> If this is too difficult, maybe the integration time can be increased to 
> >>> generate one pulse every 10second or every 100,000,000.00 cycles?
> >>> 
> >>> Finally, is a square 10Mhz reference any better in this case than a 
> >>> sinusoidal input for generating the PPS?
> >>> 
> >>> Thanks,
> >>> Jerome
> >>> 
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