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crystal & operating freq. concept

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malhar gurjar

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why operating frequency is always half of crystal frequency..?

plz give me ryt ans..as soon as possible ..
 

Hi Malhar
why operating frequency is always half of crystal frequency..?
Click to expand...
Operating frequency of a crystal ? in what circuit ? and who told this ? imagine that you have a crystal , it can work from it's fundamental up to some overtone harmonic . it is my first time to hear that it can work and f/2 . perhaps i didn't get your mean accurately ?
Best Wishes
Goldsmith
 
It's not always, just for some processor families, e.g. PIC that have fcy = fclk/2 (unless using a PLL). It's a matter of processor core design.
 
oh sorry i just forgot to write dat m asking 4 microprocessor 8085..
n m sry 4 dat..bt in 8085 operating frequency is half of crystal frequency..now tell me ur opinion...
 

According to the original 8085 data sheet, an instruction cycle takes four periods of the clock. This can be imagined as four execution phases. The external (usually crystal oscillator) input is additionally divided by two, I guess to get a clear 50 % duty cycle, possibly also for better availability of higher frequency crystals ( they are smaller).
 
I think, Tosc=1/Fosc
 

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