oscillator for micro controller

Discussion in 'Embedded Systems and Microcontrollers' started by SamK, Dec 25, 2010.

  1. SamK

    Thread Starter New Member

    Oct 24, 2010
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    hi all, i am using an AT89c55wd uC which has an on chip oscillator according to the datasheet, what id like to know is, is there a default freq. that its auto. set up at...i have a 12MHz crystal and i want to run at this freq. do i need the crystal or can i set up the chip for this without the crystal....ha i know its xmas mornin but these things run through my head all day everyday...merry crimbo to all!!!
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    What does the datasheet say? If a mcu has an on-board osc, usually yu do not need any other supporting components. The on-board osc should have a range of frequencies.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    The internal Oscillator is set by "fuses" either through program definitions or at the time you flash the uC with the code.

    I don't recall offhand what the options are for Atmel, but the datasheet should let you know.

    The internal oscillator may be 4Mhz-20Mhz, but not as precise/stable as an external crystal oscillator. This is important if you are using the uC as a timebase or when getting small and accurate time measurements, such as 2.5000 milliseconds.
     
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