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
    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

    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
    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.