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OT: Latter 18F parts very fussy about crystals

 
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Will Reeve



Joined: 30 Oct 2003
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Location: Norfolk, England

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OT: Latter 18F parts very fussy about crystals
PostPosted: Thu Feb 16, 2006 11:22 am     Reply with quote
Just spent quite a while getting my 18F6310 working with a 20MHz AT cut crystal. Took 2k of series resistance and a drop in capacitance to get it to oscillate. This part can apparently drive a 40MHz crystal and has a PLL.
The old 16F877 would happily drive anything you threw at it with any cap/resistance (within reason!). I sometimes wonder if Microchip has gone backwards!
I am worried now about the repeatability in production versions!
Ttelmah
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PostPosted: Thu Feb 16, 2006 3:08 pm     Reply with quote
There were a lot of posts about this, when the first parts with PLL's appeared. Basically, chips with PLL's are very much more fussy about not having their inputs overdriven. The greater amplifier gain on parts supporting even higher speed crystals, makes this more of a problem.

Best Wishes
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