Probotector II NTSC/Dendy patch

[NewRisingSun]

Some people like the robots so much that they want an NTSC/Dendy patch for the European version of Contra II. Patching is needed for the music to have the correct pitch relationship of square/triangle channels versus DPCM Orchestra Hits on both NTSC and Dendy, and have the music at the correct speed on NTSC.

The first patch creates an Dendy version (pitch correction only), the second create an NTSC version (pitch+speed correction); both are to be applied to the PAL ROM image file.

[aiko1125]

I have always wanted this! But, what are the differences between PAL and Dendy?

[tepples]

NTSC NES/FC:
3 dots per CPU cycle (therefore 113.6667 per line)
NMI at line 241 (21 before start of next picture)
NTSC-like noise and DMC period tables

PAL NES:
3.2 dots per CPU cycle (therefore 106.5625 per line)
NMI at line 241 (71 before start of next picture)
PAL NES-like noise and DMC period tables

Dendy and other PAL famiclones:
3 dots per CPU cycle (therefore 113.6667 per line)
NMI at line 291 (21 before start of next picture)
NTSC-like noise and DMC period tables

The regional differences that most affect game compatibility are CPU cycles per scanline and time from NMI to start of picture. Famicom games using mappers with an M2-dividing timer (notably FME-7 and VRC4/6/7) rely on these aspects, as do games using constant-timed NMI handlers (such as Balloon Fight and Battletoads) or any discrete logic or MMC1 game with multiple scroll splits (Spartan X/Kung Fu, 3D Battles of World Runner, Highway Star/Rad Racer). Thus for the purpose of game-visible timing, PAL famiclone timing is closer to that of a Famicom in these two respects than PAL NES timing.

See also Cycle reference chart

[tokumaru]

Pirates: adapting the Famicom hardware for PAL better than Nintendo themselves.