How to choose prescale and postscale of timer2 for PIC18F252

Discussion in 'The Projects Forum' started by mermaid09, Dec 25, 2009.

  1. mermaid09

    Thread Starter New Member

    Nov 21, 2009
    Hello everyone..
    I need somebody to help me to explain about the prescale and postscale for timer2.
    I am not very clear how to choose the prescale and postcale. My circuit using 20Mhz external oscillator on the pic18f252.
    Please help me..
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Prescaling simply reduces the frequency of the input pulses by a known factor. If 20 MHz is too much, apply the pulse train to an external counter so it does a divide by 20 operation. Then, the input pulses are at a frequency of 1 MHz.

    Postscaling is translating the count into engineering units, like RPM. That just relates the value in the counter to some meaningful figure.
  3. mik3

    Senior Member

    Feb 4, 2008
    Go to

    Go to datasheets and choose PIC18F252

    You will find many applications notes there. There should be one for timer 2.