Re: Converting a Commodore 64 from NTSC to PAL

From: Rob Clarke <>
Date: Fri, 13 Apr 2012 14:48:43 +0200
Message-ID: <>
> On 13.04.2012, at 09:04, Gábor Lénárt wrote:
>> Btw, as far as I know (or am I wrong?) some timing is based on the
>> frequency
>> of the AC 9V. So in the USA it's 60Hz, where here it's 50. Just
>> converting
>> the voltage would work I guess, but the frequency difference can cause
>> different timing. I can't remember now where it's used though, if it is
>> at
>> all. Maybe does CIA use it? My assumption that NTSC C64s generated NTSC
>> video signal and except 60Hz, and PAL ones except 50Hz, so not only the
>> video signal and the PSU input AC voltage is the difference
> No, all of the video timing is generated by the VIC and uses only the dot
> clock and color clock derived from the master crystal (14.318MHz for NTSC
> or 17.7xxx MHz for PAL) for everything including the CPU clock. That's why
> you need different VICs for NTSC and PAL.
> The 50Hz or 60Hz derived from the 9V AC from the power supply is only used
> for the 2 CIAs and there only for the TOD which, as far as I know, is not
> used by the Basic or Kernal at all.
> That doesn't mean that there won't be software that will detect whether
> it's running on PAL or NTSC, then uses the TOD and sets the divider Bit
> for the TOD wrong on a PAL C64 running in the USA.
>  Gerrit
>        Message was sent through the cbm-hackers mailing list

The TOD clock on the CIA's has a control bit which indicates whether the
clock signal is 50 or 60 hz. I could not for the life of me remember how
this gets set by the Kernal. The CBM-II's had a jumper on one of the TPI's
but AFAIK, the only jumper on the 64 boards was only for the clock
divider, and not hooked up to any of the control ports. As the 64 kernal
was region agnostic, how did it set the 50/60hz control?


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Received on 2012-04-13 13:00:40

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