Changes
Z80
,/* Internal state */
Normally, you never see the content of this register. But it leaks the info through in case of the BIT b,(HL) instruction. [https://zx-pk.ru/attachment.php?attachmentid=2989 Source]
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| Q || 8-bit || Internal register where it assembles the new content of the F register, before moving it back to F || When On Zilog Z80, when the instruction doesn't modify the flags, this register is reset instead (or in case of NEC CPUs, set to some partially undefined values).
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. Only a 1-bit F-changed flag , indicating whether the previous instruction computed flags, is needed to emulate the behaviour of SCF/CCF. Also note that POP AF and EX AF,AF' do not compute new F values. [https://github.com/hoglet67/Z80Decoder/wiki/Undocumented-Flags#scfccf Source]
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| IR (Instruction Register) || 8-bit || Holds the opcode of the currently executing instruction || Internally used, not accessible by the programmer
