* The NOP instruction takes 2 full-cycles. This is the minimum amount of cycles an instruction can take. It is necessary because, while the instruction itself does nothing, it still has to increment the 16-bit PC register.
* The alternate NOPs are not created equal. Some have one- or two-byte operands (which they don't do anything with), and they take different amounts of time to execute.
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== Compared behaviour ==
* 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.
* The 6502 uses only one addressing mode per instruction, while the Z80 can combine two different addressing modes within a single instruction.
* The 6502 post-decrements on PHA and pre-increments on PLA, while the Z80 pre-decrements on PUSH and post-increments on POP.
* The 6502 saves flags automatically during interrupts; while the Z80 requires PUSH AF and POP AF.
* The 6502 only updates flags that are directly relevant to the operation's result. For example, EOR doesn't conceptually involve a carry, so the Carry flag is left untouched. On the Z80, XOR always clears the Carry flag to ensure a clean flag state.
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