Changes
Z80
,/* Internal state */
|-
| WZ || 16-bit || Internal temporary register pair. Also known as MEMPTR || Used for memory and address calculations.
Normally, you never see the content of this register. But it leaks the info through to F5 and F3 in case of the BIT b,(HL) instruction. [https://zx-pk.ru/attachment.php?attachmentid=2989 Source]
|-
| Q || 8-bit || Internal register where it assembles the new content of the F register, before moving it back to F || On Zilog NMOS Z80, when the instruction doesn't compute new flags, this register is cleared instead. But not on NEC NMOS Z80. And CMOS Z80 behave in a different way too.
Normally, you never see the content of this register. But it leaks the info through in case of the SCF/CCF instructions. [https://worldofspectrum.org/forums/discussion/41704 Source]
Emulating Q is not strictly necessary. A 1-bit flag, indicating whether the previous instruction computed flags, is enough to emulate the behaviour of SCF/CCF. [https://github.com/hoglet67/Z80Decoder/wiki/Undocumented-Flags#scfccf Source]
