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Are any of these crystal frequencies 'special'?

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astronomerroyal

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Some time ago I bought an assorted pack of crystal oscillators. I was wondering if any of these frequencies had any special place in the world of (PIC) microcontrollers. 8MHz is the only familiar frequency.

in Hz.

4332K
4500K
5.25M
5.76768M
6.176M
8.0M
13.50M
14.31818M
14.7456M
16.6344M
18.432M

I also have some >>20MHz, so I was wondering if they were geared towards radio people, but since I currently don't do that I thought I'd ask here. I assume I can use any of these with PICs rated up to 20MHz.

Thanks.
 
Ya You are right. You can use any value of the crystal listed above with PICs rate up to 20MHz. Everytime you use a different crystal you need to reprogram the PIC.

Geared towards radio people ?? NO idea about that sorry
 
In general, it will probably run with the same code but different crystal. Perhaps you meant that you have to change any timing related code to get correct results. You might need to change the osc config bits as well if going from a 4 mhz to 20 mhz. Also, on the 18F line, you might have to change the PLL setting.

Some crystal frequencies are selected to divide down evenly for things like baud rates (18.432M). 13.5M is a from DVD player's master clock. 14.31818 is common on VGA cards and used for NTSC color subcarrier (div by 4).

edit: by the way, you can overclock a lot of PICs. The guys are sparkfun have an article on it. They got to something like 32mhz before they gave up. I don't know if it causes damage - probably not - but I'd check out all the functions to make sure they aren't affected.
 
Last edited:
Some crystal frequencies are selected to divide down evenly for things like baud rates (18.432M). 13.5M is a from DVD player's master clock. 14.31818 is common on VGA cards and used for NTSC color subcarrier (div by 4).

Ah, very interesting. Thanks.
 
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