Re: NTSC VIC-II timing

Date: Wed, 21 Jun 2017 18:12:12 +0200
Message-Id: <>
> On 2017-06-21, at 17:01, wrote:
>> According to the famous document by Chris Bauer, there are three timing
>> variants of the VIC-II. While PAL is always 63 cycles per  line, with NTSC
>> there can be either 64 or 65 cycles per line and I am in fact able to
>> reproduce the difference with -model ntsc and -model oldntsc in the current
>> VICE.
>> The question (before I spend weekend on trial'n error counting cycles and
>> possibly reinventing the hammer ;-) is: do we have ane established,
>> reliable software method for detecting which NTSC VIC-II is installed in
>> the machine? I guess it must have been done multiple times by now and used
>> in some NTSC games/demos..
> most demos or games probably dont care about detecting the difference - as the 
> 64 cycle VIC is extremely rare.

Maybe I am impractical indeed, yet I can't envision a commercial product (game f.e.) that would just break because the machine has a different but still valid VIC chip inside.

> however, iirc on codebase there are some detection routines.

I found a routine on codebase that is supposed to distinguish between the NMOS and HMOS variants of the PAL VIC:

interesting in its own if it works, but that's not what I need.

> basically just count the cycles for a line (or a frame) using a CIA timer.

Exactly what I meant with spending lots of time counting cycles ;-)

SD! -

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Received on 2017-06-21 17:00:02

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