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Crystal and ntsc — Parallax Forums

Crystal and ntsc

TransistorToasterTransistorToaster Posts: 149
edited 2007-04-14 01:19 in Propeller 1
Hello,
I would like to know how sensitive the NTSC chromaburst frequency is to the Propeller crystal frequency? Can I use an 80MHz oscillator and still have the TV functions work? Are there certain frequencies that are recommended or that should be avoided?
Frank

Comments

  • LeonLeon Posts: 7,620
    edited 2007-04-13 20:36
    Just use a 5 MHz crystal with 16x PLL. That's what the TV examples use.

    Leon
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-04-13 20:39
    TransistorToaster said...
    Hello,
    I would like to know how sensitive the NTSC chromaburst frequency is to the Propeller crystal frequency? Can I use an 80MHz oscillator and still have the TV functions work? Are there certain frequencies that are recommended or that should be avoided?
    Frank
    In general the colorburst frequency cannot have more that a 1% deviation in frequency, but the Propeller code will work for a wide variety of frequencies if you accurately specify the frequency it is running·at in the CON directives.

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    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • rokickirokicki Posts: 1,000
    edited 2007-04-13 21:36
    Has anyone successfully generated TV output while running the propeller at less than 80MHz? Thanks!
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-04-13 22:41
    I just successfully tested Graphics_Demo at an input of 1.6MHz or 25.6MHz system clock, the graphics part is slower but the TV is still rock solid.

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    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.

    Post Edited (Paul Baker (Parallax)) : 4/13/2007 10:46:02 PM GMT
  • HarleyHarley Posts: 997
    edited 2007-04-13 23:35
    What an amazing chip the Propeller is, if what I understood Paul to say.
    That the clock input was varied over that range.
    Impressive design of that silicon to be so adaptable. yeah.gif

    Chip, and Company, did a highly impressive design for us to play with. Congratulations, guy!

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    Harley Shanko
    h.a.s. designn
  • TransistorToasterTransistorToaster Posts: 149
    edited 2007-04-14 01:19
    >I just successfully tested Graphics_Demo at an input of 1.6MHz or 25.6MHz system clock, the graphics part is slower but the TV is still rock solid.
    Wow, thanks for trying that out. I'll have to analyze more for myself how the color can still work with all kinds of clock inputs. I was expecting jitter problems and color to not work properly for various clocks.
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