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NES 2.0 "Official" Specification
http://forums.nesdev.com/viewtopic.php?f=3&t=2090
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Author:  VEG [ Sun Oct 09, 2016 11:29 pm ]
Post subject:  Re: NES 2.0 "Official" Specification

My interpretation (with the proposed Dendy flag):
Code:
Byte 12:
7       0
---------
xxxx xDBP
0000 0000 - NTSC only
0000 0001 - PAL only
0000 0010 - Supports NTSC and PAL, but NTSC is preferred
0000 0011 - Supports NTSC and PAL, but PAL is preferred
0000 0100 - Dendy only, but if Dendy mode isn't available in the emulator, use NTSC
0000 0101 - Dendy only, but if Dendy mode isn't available in the emulator, use PAL
0000 0110 - Supports Dendy, NTSC and PAL. Dendy mode is preferred, but if Dendy mode isn't available in the emulator, it will use NTSC
0000 0111 - Supports Dendy, NTSC and PAL. Dendy mode is preferred, but if Dendy mode isn't available in the emulator, it will use PAL
It's simple and almost all cases are covered. The only drawback that I can see is that we can't indicate that the ROM supports, for example, Dendy and NTSC modes only. But I don't know why it may be needed.
IMHO, the bit B is not a very useful flag. I doubt if it is used by any emulator.

Author:  VEG [ Sun Oct 09, 2016 11:38 pm ]
Post subject:  Re: NES 2.0 "Official" Specification

Myask wrote:
Still think that NTSC should have its own bit instead of this extensibility-poor "both" here. A Dendy bit would be fine too.
The idea to have some kind of mask of which systems are supported in this ROM is nice. So, it will be bits N for NTSC, P for PAL, and D for Dendy. As the result we will be able to set only P and D, or N and D, or N and P, or all of them. Also we have to have a way to tell the emulator which mode is preferred. For example, Unchained Nostalgia supports PAL, NTSC and Dendy, but Dendy mode is preferred, and if it is not supported, NTSC mode is preferred.

We have to take into account how B and P bits are treated by modern emulators. As far as I understand, they use NTSC when bit P is clear, and PAL when bit P is set. Am I right? How modern emulators treat the B bit? If they ignore this bit, maybe it is possible to change the meaning of this bit.

Author:  VEG [ Mon Oct 10, 2016 1:46 am ]
Post subject:  Re: NES 2.0 "Official" Specification

NSF spec:
Quote:
$07A 1 BYTE PAL/NTSC bits
bit 0: if clear, this is an NTSC tune
bit 0: if set, this is a PAL tune
bit 1: if set, this is a dual PAL/NTSC tune
bits 2-7: not used. they *must* be 0

NSFe spec:
Quote:
$0006 1 BYTE PAL/NTSC bits
bit 0: if clear, this is an NTSC tune
bit 0: if set, this is a PAL tune
bit 1: if set, this is a dual PAL/NTSC tune
bits 2-7: not used. they *must* be 0

So, this byte is similar everywhere and new extension will be applicable to these formats also =)

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