Processor frequency and Crystal frequency???

[Ram Prasadh]

(IN MPLAB),What is the difference between the processor frequency which we set in the debugger settings and the crystal frequency from the oscillator? what is the work of these two frequencies?Is there any criteria of which one should be higher or lower?

 

[assasinsareus]

Hello,

I'm assuming that crystal frequency is the frequency of your crystal oscillator eg 20MHz for a 20MHz crystal. The Processor frequency is the crystal frequency divided by the processor's crystal frequency to program frequency difference. On a 10,12,16,18 series PIC the processor frequency is always 4 times slower then the crystal frequency.

Eg A PIC16 using a 20MHz crystal will actually be running at 20/4=5 MIPS (Million Instructions Per Sec).

---------- Post added at 12:45 ---------- Previous post was at 12:44 ----------

dsPIC30 / 24 have a 1:4 ratio
dsPIC33 have a 1:2 ratio

See 001tech.co.uk for more details and embedded projects.