* INI/IND/INIR/INDR decrease B after storing the byte from the hardware port into memory. And OUTI/OUTD/OTIR/OTDR decrease B before sending the memory byte to the hardware port. [https://www.cpcwiki.eu/forum/programming/z80-documentation-errors/ Source]
* All PUSH and POP instructions utilize a 16-bit operand and the high-order byte is always pushed first and popped last. PUSH HL is PUSH H then L. POP HL is POP L then H.
* The Z80 pre6502 post-decrements on PUSH PHA and postpre-increments on POPPLA, while the 6502 postZ80 pre-decrements on PHA PUSH and prepost-increments on PLAPOP, making them behave in opposite ways.
* The 6502 saves flags automatically during interrupts; while the Z80 requires PUSH AF and POP AF.
* The 6502’s Decimal (BCD) mode automatically adjusts ADC and SBC results, while the Z80 requires a DAA instruction after each BCD addition and subtraction.