Friend of mine (who knows I really like Zanac) pointed me to this today:
http://tcrf.net/Zanac_%28NES%29
Note that to get Debug mode to work, you have to use the US/NTSC cart/ROM (not sure about EU/PAL) with a Famicom keyboard.
Regarding why the Japanese cart/ROM doesn't work for this -- I imagine this is what happened:
The game was finished (with Debug mode left possible) and US ROMs submit to Nintendo for review + signoff was given. I'm sure someone at some point said "Uh, what about Debug mode?" and the reply was "the NES doesn't have a way to use the Famicom keyboard". If I remember right, submitting ROMs to Nintendo for review/approval was a timely process and cost money, so it didn't really make sense to "recall" the previous submission just to remove some code that could (potentially) never be abused. Then, of course, for the Japanese release, the code was later either removed, NOP'd out, or some assignments/changes of some kind to get rid of the Famicom keyboard input.
A binary comparison and commented disassembly of the differences would be really interesting (mainly to see what all they did to get rid of Debug mode on the Japanese release).
http://tcrf.net/Zanac_%28NES%29
Note that to get Debug mode to work, you have to use the US/NTSC cart/ROM (not sure about EU/PAL) with a Famicom keyboard.
Regarding why the Japanese cart/ROM doesn't work for this -- I imagine this is what happened:
The game was finished (with Debug mode left possible) and US ROMs submit to Nintendo for review + signoff was given. I'm sure someone at some point said "Uh, what about Debug mode?" and the reply was "the NES doesn't have a way to use the Famicom keyboard". If I remember right, submitting ROMs to Nintendo for review/approval was a timely process and cost money, so it didn't really make sense to "recall" the previous submission just to remove some code that could (potentially) never be abused. Then, of course, for the Japanese release, the code was later either removed, NOP'd out, or some assignments/changes of some kind to get rid of the Famicom keyboard input.
A binary comparison and commented disassembly of the differences would be really interesting (mainly to see what all they did to get rid of Debug mode on the Japanese release).