out (c),0 [ED 71] can actually write a value different than 0 about opcode-table

[sverx]

I wouldn't know what I could suggest. AFAIK the only difference in the processor's behavior is this one.

[sverx]

Anyway, note that this difference is not specific to the SEGA Game Gear, it's about CMOS/NMOS Z80 processors.
Here's a post from benryves on Reddit -> https://www.reddit.com/r/Z80/comments/hwglc4/comment/fz0kt7w/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button which links to this document -> https://worldofspectrum.org/z88forever/dn327/z80undoc.htm on WorldOfSpectrum.org, I hope it helps.

[dt-anchorzero]

Thanks @sverx, I'll make a note of that.

What's a good reference for the behavior on the SEGA Game Gear?