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deeptoaster / opcode-table

A set of extensible tables for displaying details of machine instructions for Z80 and other architectures
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out (c),0 [ED 71] can actually write a value different than 0 #9

Open sverx opened 1 month ago

sverx commented 1 month ago

The undocumented [ED 71], albeit commonly called out (c),0, can actually output a value different than zero depending on the implementation - for instance on the SEGA Game Gear (CMOS) it outputs 0xFF instead. I think there's should be a note in the description.

dt-anchorzero commented 1 week ago

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

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

sverx commented 1 week ago

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

sverx commented 1 week ago

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.