
Convert a Commodore 64 from NTSC to PAL Format - erickhill
http://biosrhythm.com/?p=1420
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weinzierl
> With it’s different VIC-II chip generating a different master clock signal,
> the PAL C64 has a few more cycles available per frame than the it’s NTSC
> counterpart.

Just for additional clarification: If I remember correctly the C64 had only a
single quartz. All clock signals were derived from that single quartz. That
meant that also the clocks driving the raster beam were derived from that
single quartz.

As a consequence the main processor in NTSC and PAL versions ran at different
frequencies. The PAL version was 0.98 MHz and if memory serves me correctly
the NTSC version was slightly above 1 MHZ.

Even back then some people overclocked their machines, but it was different
than today. You had a hardware switch for the frequency and when you were in
fast mode no IO was possible. No video, but also no serial communication. To
see the results of your calculation you had to switch back to slow mode.

~~~
emptybits
> All clock signals were derived from that single quartz. That meant that also
> the clocks driving the raster beam were derived from that single quartz.

Yes, and that VIC clock also drives the SID sound chip. So while the same code
will play a song back "in tune" (relative pitch) on both a PAL and NTSC C64,
it will be tuned lower (absolute pitch) on a PAL C64. Think of it like the
concert pitch difference between A = 443 Hz (Germany -- common) and A = 430 Hz
(Verdi tuning a.k.a. Schiller Institute -- uncommon).

To play the same absolute pitch on both a PAL and NTSC, code _could_ use an
alternate lookup table to map a note to different SID frequency register
values for PAL or NTSC. In practice, I don't think this was done, but someone
can correct me. What was, sometimes, done was skipping every 6th frame of a
raster vblank music playback routine on an NTSC C64 (@ 60 Hz) to match the
_tempo_ (not pitch) of the same song played on a PAL C64 (@ 50 Hz).

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DanBC
The site RetroRGB has a bunch of mods for games consoles to convert them to
(or improve their) RGB output.

[http://retrorgb.com/](http://retrorgb.com/)

It's pretty interesting.

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jhallenworld
I'm amazed they made different chips for PAL vs. NTSC instead of having a
jumper or pin to select the mode. Same thing on Atari 800.

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Annatar
I want to keep my C=128D NTSC for testing that my code works on both PAL and
NTSC correctly, but I'm running on 50Hz, 220-240V. What in the power supply do
I have to replace?

~~~
dfox
As the C128D power supply is based on mains transformer, first thing you need
to replace is said mains transformer. It's probably easier to just remove the
whole original power supply and replace it with some small industrial 5VDC
SMPS and 9V transformer (assuming that nothing depends on the frequency of the
9VAC input, which from looking at service manual seems to be the case).

~~~
rzzzt
The 6526's time-of-day clock uses it, on the C64, aftermarket or hobbyist
power supplies that leave it out make the variables TI and TI$ stop updating.

