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Hi all, Purchased a 40MHz oscillator (sp) crystal for use with my 18F252. I read else where on this forum that there may be an internal clock in the 18Fx series. Can anyone give me a circuit diagram of where to put my crystal, or do I even need to use one?
Trust
You wasted your money. I'm sorry to tell you it's not going to run with a 40MHz crystal or external oscillator at that speed.
To run at 40MHz, use a 10MHz crystal and set the internal PLL to x4.
Make friends with section 2 of the Datasheet (it also shows you how to hook up your Oscillator, Crystal, resonator or whatever and what loading capacitances you might need.
I'm going to cry soon, this damn PIC takes so much work and this is all before I've properly tested it! OK so I will be getting a 10MHz crystal instead. From the datasheet it says I need two capacitors (C1 and C2) from the link bellow.
http://img.photobucket.com/albums/v4...ytrust/ex3.jpg
Can you please suggest values I should get for it to work at 10MHz and will there be any other cruticial components just to get the pain in the ass PIC working?
thank you
It says 10-22pF, so pick 15pF as a starter... kinda midway...
It's not a critical PIC, hell, it'll work from a piece of wet string in RC mode. Anything will get this going... 4Mhz Ceramic resonator, whatever... remember it's a replacement for the 16F87x when you run out of steam... you drop this PIC in it's place, and as long as you didn't have a flaky design to start with, away you go...
Right, got the capacitors and the 10MHz crystal, one last question, do these quatz crystal things have a polarity or have to go in a specific way. I mean on the case I find no markings for polarity and in the datasheet nothing also, so just double checking before I risk blowing it up!
absolutely not. like ceramic cap or crystal resonator. No polarity, no nothing.Quote:
do these quatz crystal things have a polarity or have to go in a specific way.
regards