Re: Questions about pal clocks

From: Marko Mäkelä (
Date: 2001-11-22 16:02:29

On Thu, 22 Nov 2001, Jozsef Laszlo wrote:

> Probably I'm worng, but the TVs have some tolerance for the scan line
> timings. In theory one scan line must be 64us long, but if you calculate
> the normal VIC timings, you'll see that is not this value in the C64:
> DOTcloks*540 = one scan line,  (1/7.88Mhz)*540 = If I used
> 8Mhz for the DOT clock, it would be 67.5us.
> (Correct me if I'm worng, please)

The 540 above should be 504 (which is 63*8).  With a 8 MHz dot clock,
you'd get 63 µs (microseconds) per line instead of the 64 specified for
PAL-B systems.  With the 7.881984 MHz dot clock (17.734472/18*8), one scan
line takes 63.94 µs, which is 1.50% too fast.

Yes, you're correct that very few 8-bit Commodores follow the standard.  
Only the NTSC VIC-20 can produce an interlaced composite video signal, and
also there the frequencies are off the specifications.


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