Output of oscillator of MCU

Discussion in 'General Electronics Chat' started by aamirali, Feb 24, 2013.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    1. Oscillator have 2 pin. What is there output voltage & waveform if I put probe on CRO., consider 20Mhz on 89C51. It must be sine wave.

    2. I put a probe on XTALIN w.r.t ground, with power on to MCU, waveform is getting distorted & no signal shown. Might be capacitance of my probe is too large.

    3. Then I put a probe on XTALout w.r.t ground, then a +ve dc level shifted sine wave is shown.

    4. Then I put a probe on XTALIN & ground reference of CRO on XTALOUT,

    I got wierd waveform.
  2. antonv


    Nov 27, 2012
    A crystal oscillator is designed to function properly with only the capacitance that is present on the board. Anything else you connect to the input will change its frequency or stop the oscillator. So you are correct about your probe having too much capacitance.
    Measuring the output with respect to ground will work to let you see if the oscillator is running at about the right frequency.
    I am not aware of any reason for measuring the input with respect to the output.
  3. aamirali

    Thread Starter Member

    Feb 2, 2012

    Just want to note phas diff b/w two.
    I checked with 10x probe & its 180.