:| Se~~~~~~ Ga~~~~~~~
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Domestic mode = Japan
Export mode = Not Japan (Europe or USA)
Mega Drive 1 boards revisions work like this:
IC BD M5 VAxx
VA0 = no VAxx, Japan only
VA1 = Japan only
VA2 = Rare in USA (IC BD M5 VA2 USA)
VA3 = Should be common in USA (IC BD M5 VA3 USA)
VA4 = Should be common in USA (IC BD M5 VA4 USA)
VA5/6 = IC BD M5 (VA5 does not exist in USA but has no TMSS while in domestic mode)
Details here:
http://segaretro.org/Mega_Drive_PCB_revisions
The guy on the video comments that sound is bad on all newer units but there are units with TMSS and good sound (USA VA6, for example)
Very late model1 units (VA7) have Mega Drive 2 chips in them and those do have the bad sound.
Program wise to pass TMSS check all you need is have "SEGA" ASCII written at offset 0x000200 of the ROM cartridge.
And these consoles require the binary data for "SEGA" to be written at a specific register on the chipset otherwise the chipset blocks the CPU from receiving the interrupt signal from the video chip.