Dario Greggio wrote:
> Jan-Erik Soderholm wrote:
>> No, the datasheet(s) does.
>>
>> See the parameter F11/Fsys (On-Chip VCO System Frequency):
>>
>> 18F1230: Min/Max : 16/40 MHz.
>> 18F4550: Typ: 96 MHz (*no* min/max specified)
> 
> I see :)
> you're "deducing" this fact from another one :))
> I don't know, of course there may be PLLs which do work @ one fixed 
> frequency, and others which can multiply whatever.
> 
> I'll try to make a test with a 6MHz XTal.
> 

Well, all PLLs have to work at a variable frequency, right? Otherwise,
what's the point of a crystal - just let the PLL free-run and let it
come up with a perfect 20ppm output (not!).

The question is how much variation around the natural frequency can the
4550's PLL tolerate. It's specced at 4Mhz input because that's what the
USB peripheral needs (48Mhz), but that doesn't mean it can't operate at
other frequencies. One thing's for sure though, if Jinx had it running
at 8Mhz input with PLLDIV=1 and CPUDIV=2, the pic isn't going to like
the 96Mhz core clock speed (and the PLL probably won't like to output
192Mhz anyway).

-- 
Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/marcan.asc

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