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External Oscillator and Prop — Parallax Forums

External Oscillator and Prop

Matt32493Matt32493 Posts: 23
edited 2010-11-25 21:10 in Propeller 1
How would one attach an external Oscillator to the propeller chip? I have the 5Mhz Oscillator from parallax and i can not get it to work.. nor any documentations with it... Thanks
Matt

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-11-25 19:30
    Do you mean a 5MHz crystal? That's what Parallax sells. Those are just connected between the XI and XO pins. If you really mean an external 5MHz oscillator, these are a combination of a crystal with a little logic circuitry, usually all packaged together in a module. These usually have a single output pin which would be connected to the XI pin. The XO pin would not be connected.
  • Matt32493Matt32493 Posts: 23
    edited 2010-11-25 20:30
    Yes, it is the crystal. And i have tried connecting it to XI and XO, and none of my programs work using that configuration. Using:

    _clkmode = XINPUT

    No program runs, not even just setting outputs..
  • User NameUser Name Posts: 1,451
    edited 2010-11-25 20:41
    What board are you using? If it's homebrew, the problem may not be the crystal.
  • Mike GreenMike Green Posts: 23,101
    edited 2010-11-25 21:01
    XINPUT is for use with an external oscillator only. A crystal is not an external oscillator. A crystal depends on a separate oscillator circuit which is furnished by the Propeller if you use clock modes XTAL1, XTAL2, or XTAL3. See the section of the Propeller Manual on the CLKSET instruction for details. If you're using an external 5MHz crystal, you need to provide constant definitions for:

    _xinfreq = 5_000_000
    _clkmode = XTAL1 + PLL16X

    The PLLnnX is used to specify the crystal frequency multiplier to produce the system clock. PLL16X will multiply the 5MHz to produce an 80MHz system clock which is commonly used.
  • Matt32493Matt32493 Posts: 23
    edited 2010-11-25 21:10
    Thank you much. I misunderstood the Prop manual. Works great. Thanks Again.
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