1.13) What issues surround NTSC vs PAL versions of the 8-bit Atari?

Subject: 1.13) What issues surround NTSC vs PAL versions of the 8-bit Atari?

Contributors to this section:
Wayne Booth, Graham Thornton, Brent Buescher Jr., Thomas Richter, Jindroush

Some quick definitions first:

NTSC standard: Abbreviation for "National Television Standards Committee"
TV signal standard used in North America, Central America, a number of South
American countries, and some Asian countries, including Japan.
525 lines per frame
60 half-frames per second (interlaced) = 60 Hz
Complete frame refreshed 30 times per second

PAL: Acronym for "phase alternation by line"
TV signal standard used in the United Kingdom, much of the rest of western
Europe, several South American countries, some Middle East and Asian
countries, several African countries, Australia, New Zealand, and other
Pacific island countries.
625 lines per frame
50 half-frames per second (interlaced) = 50 Hz
Complete frame refreshed 25 times per second.

PAL-M: A modified version of PAL, used in Brazil.

SECAM: Acronym for "systeme electronique couleur avec memoire"
TV signal standard used in France, eastern European countries, the former
USSR, and some African countries.
625 lines per frame
50 half-frames per second (interlaced) = 50 Hz
Complete frame refreshed 25 times per second.

Now then, how do the differences among 8-bit Atari computers designed for the
different world television signal standards affect users trying to use
software written elsewhere in the world?

The 50Hz vertical refresh frequency of PAL machines translates into more
vertical blank interrupt (VBI) time for demos and other computation-intensive
graphics software, when compared to the time available for VBIs on NTSC
machines with the faster 60Hz refresh frequency. So PAL demos and games that
won't work on NTSC machines are usually returning from a VBI too late. Some
also attempt to use more vertical resolution ("longer" display lists) than an
NTSC display can handle.

Note that the reverse is also true. Software using VBIs will run more slowly
on a PAL Atari than on an NTSC Atari.

Replacing the NTSC ANTIC chip in an NTSC Atari with a PAL ANTIC changes the
screen refresh rate to 50Hz, allowing most of the PAL-only European software
to run on a North American NTSC Atari. However, make sure your display device
can support a 50Hz PAL signal first! North American Atari users can also
obtain and use real European PAL Atari machines, with the same caveat
concerning the display device.

Bottom line:
Software written for NTSC machines (North America) will (almost) always work
on PAL machines (Europe), but software designed on PAL machines won't
necessarily work on NTSC machines.

Jindroush contributes: (2/26/02)
Could there be a program which runs on NTSC Atari and not on PAL Atari? Yes,
if it uses some precise timing copy protection (probably based on vblank
timing). Examples of these are Transylvania and The Quest by Penguin Software.

Thomas Richter mentions another NTSC vs PAL issue:
Another point is that the popular pseudo-colors used in the ANTIC-F (Graphics
8) mode are not colorful at all when displayed on a PAL TV, because of
differences in the color encoding for the TV. The schematics of the XL
computers include however a hack how to change the PAL version to the NTSC
version (the PAL versions include two crystals, one with 5/4th of the
frequency of the other. One is used for the system clock, the other for the
color clock), but I never dared to apply it.

And on 10/16/03 Thomas Richter answered a related question this way:
>> Note that it's typically not too hard to get an NTSC Atari to run in PAL
>> by just swapping out the ANTIC chip.
>>
>> Unfortunately, some demos actually check the OS ROM for a particular
>> value to see if it's a PAL machine or not, and then refuse to run if
>> they are. *grumble* I'd rather have a warning than a refusal. :^P

> As far as I am aware, the only value to tell a PAL from a NTSC machine is in
> GTIA. Maybe swap that one as well and see what you get

Absolutey correct, GTIA keeps the PAL/NTSC register and the Os rom reads it
from there. However, besides the GTIA PAL and NTSC machines differ in other
aspects. For example, on PAL machines an additional oscillator of 5/4 of the
main frequency is present to generate the color frequencies needed to drive
GTIA. There is no such circuit in NTSC Ataris. Besides, this factor of 5/4 is
also the reason why you don't get "artifacted colors" on PAL machines (or, at
least, not very good ones.)