Posted By
TLC
on 2024-03-03
14:14:05
|  Re: NTSC vs PAL compatibility
In short:
- Scanline timing is similar
- Top and bottom vertical borders have 25-25 less scanlines (roughly equally, but I don't remember exact details). All in all - you have 50 less border scanlines per frame.
- Kernal ROM is different (--> different signature bytes, different init value for $ff07). Yes, you'll find $48 in $ff07 on an NTSC machine (after reset).
- The visible screen part is unaffected (as much as $ff0b, $ff1a- $ff1f is concerned). That's in fact true for the visible screen part plus the first few ten lines of the bottom vertical border.
Frame rate is ~ 60Hz.
There are also two aesthetic differences (maybe nothing to do about them, but they'll be there anyway). First, the visible screen area is slightly stretched, compared to that of PAL. (Think this over: you have the same sized CRT, but you display 50 less (equally spaced) scanlines, of which the "visible screen area" is still 200 lines high.) Second, the colour palette would be a small bit different to that of PAL, horizontal colour resolution would be a bit worse. Unlike in PAL, no colour averaging would happen between adjacent scanlines. (All of them consequences of PAL - NTSC colour encoding differences.)
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