Hi,

Thanks for the comments, data sheet seems reluctant to come out and admit it won't run in HS>25Mhz!!
So I may be on the wrong route trying run with a 40Mhz crystal. So here is a more detailed explanation of my problem, as I am running short on ideas!!

I need to run at 40Mhz for my project, until now I have been using a HS/PLL mode with a 10MHz crystal without any problems. I have setup the crystal in an external PLL to lock to a 15.625Khz video sync signal (using Elantec EL4583 Genlock IC and external divider), this was required to allow me to genlock to an incoming video signal and then generate my own sync to supply another camera and add on screen graticules to the image going to a monitor.

A problem I have found is that when the 18F252 locks its internal PLL to the incoming 10Mhz it can be locked in anyone of 4 positions relative to the 10Mhz, which is obvious as it will have 4 periods to 1 of the incoming signals.
What i see with my application is that only 1 of these 4 positions will work correctly. Not easy to explain the fault but in the other 3 positions I can see on the TV monitor that the vertical graticule i generate will have a kink in 1 or two places of 100ns (1 instruction Cycle). I believe that it is related to the fact that I am interrupting off the incoming horizontal sync (15.625Khz) and if the PIC PLL has locked in a 'bad' position, the relationship of the clock position to the incoming sync signal is borderline and a slight variation can cause the interrupt to a occur 1 instruction cycle earlier or later. If the the PIC PLL has locked to the 'good' position everything is solid and it works like a dream!

I am currently trying to run the PIC in HS mode with a 40Mhz crystal to avoid the HS/PLL issue, hence my first question.

Hope this makes some sense, very tricky to explain. Any ideas to run in HS/PLL or any other ideas would be very much appreciated.

So close and yet so far.........

Regards,
Daniel Sweet

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics