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TV.spin fntsc value? — Parallax Forums

TV.spin fntsc value?

jmspaggijmspaggi Posts: 629
edited 2010-09-13 05:52 in Propeller 1
Hi all,

Where fntsc and fpal are coming from? Are they calculated for 80Mhz? If my prop now run at 100Mhz, should I update that?

I tried to use a 6.25 Crystal, but the display was pretty bad so I went back to 5.

Thanks,

JM
  fntsc         = 3_579_545     'NTSC color frequency
  lntsc         = 3640          'NTSC color cycles per line * 16
  sntsc         = 624           'NTSC color cycles per sync * 16

  fpal          = 4_433_618     'PAL color frequency
  lpal          = 4540          'PAL color cycles per line * 16
  spal          = 848           'PAL color cycles per sync * 16

Comments

  • ForrestForrest Posts: 1,341
    edited 2010-09-09 19:19
    The NTSC colorburst frequency is 3.579545 MHz - or exactly twice the twice the clock frequency of my old Atari 800.
  • potatoheadpotatohead Posts: 10,261
    edited 2010-09-09 20:55
    No, you don't need to update those.

    They are constants, and are the color reference frequencies for PAL and NTSC.

    The counters are used to develop the video signal, and math is done to calculate those values from the system clock.

    Not sure why the display is bad. I run 100Mhz, 96Mhz and 80Mhz regularly...

    On PAL, PLL jitter can be at issue, but on NTSC, the displays are nice.

    Are you using broadcast??
  • jmspaggijmspaggi Posts: 629
    edited 2010-09-13 05:52
    potatohead wrote: »
    Are you using broadcast??

    If I don'T know what that mean, does it mean I'm not using it? ;)

    I'm using TV.spin.

    I only changed the number of rows and cols to feet my display.

    I just order a 6Mhz Crystal to see if it's cleaner than the 6.25 one.

    At 100Mhz, there is some diagonals lines displayed. I absolutly don't know why.

    Everything else is working fine.

    JM
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