I've been working with the 18F252 for a while, always using a 20 MHz crystal. Now i need to speed up some routines, and besides improving the code, i want to use a higher clock. The manual states that this PIC can work up to 40 MHz; it implies that using a 10 MHz clock and a internal 4x PLL the PIC can work internally at 40 MHz. Is this the only way to make it work at this speed? Can it work directly with a 40 MHz resonator?
If you can give me a hand, i'll ve really grateful.
Best regards,
Fernando
newguy
Joined: 24 Jun 2004 Posts: 1903
Posted: Thu Apr 19, 2007 8:43 am
It can't work directly with a 40 MHz crystal/resonator. You can only use crystals up to and including 20 MHz. For operation above 20 MHz you have two options: use a crystal whose frequency is 1/4th your desired frequency and use the PIC's internal x4 PLL or use an external clock souce at your desired frequency to directly drive the PIC's OSC1/CLKI pin. The #fuse for this option is EC or EC_IO (usually).
fmartinezs
Joined: 16 Aug 2006 Posts: 19
Posted: Thu Apr 19, 2007 9:32 am
Thanks!
I'll guess i'll try and find some 10 MHz xtals then.
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