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High crystal value or PLL

 
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High crystal value or PLL
PostPosted: Wed Jan 30, 2008 11:49 am     Reply with quote
Hello, what is better:
to use 4MHz crystal and PLL to get CPU at 24Mhz
or to use 24MHz crystal?
cheers
dyeatman



Joined: 06 Sep 2003
Posts: 1934
Location: Norman, OK

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PostPosted: Wed Jan 30, 2008 11:55 am     Reply with quote
It's best to use a 24MHZ oscillator can rather than an Xtal at all. However, if you use the PLL, you must use a 6MHZ xtal to get 24MHZ (it is a x4 PLL NOT x6).
Guest
PostPosted: Wed Jan 30, 2008 12:13 pm     Reply with quote
dyeatman wrote:
However, if you use the PLL, you must use a 6MHZ xtal to get 24MHZ (it is a x4 PLL NOT x6).

Are you sure?
4MHz crystal => fuses would be: XTPLL,PLL1,CPUDIV3
which yields 24MHz for peripherals and CPU.
Isnt that correct?
Guest
PostPosted: Wed Jan 30, 2008 12:16 pm     Reply with quote
oh, it applies for 18F2455 (with USB) only . It is quite different for 18F2420 as I can see.
You are right then.
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