Changes
/* Instruction Execution Sequence */
#Memory Write / I/O Write (if needed)
#At the end of every instruction, the IRQ (if the interrupt disable flag is clear) and NMI pins are checked.
For example, with M[$42]=$80 and M[$43]=$10 and Y=$F1, the instruction LDA ($42),Y will execute as follow:
*T0: Fetch opcode $B1 (LDA (zp),Y) from memory
*T1: Fetch operand byte $42 (zero page pointer address)
*T2: Get low byte from zero page ($80)
*T3: Get high byte from next zero page location ($10)
*T4: Add Y-register value ($F1) to form address $1171
*T5: Handle page boundary crossing (since $1080 + $F1 crosses a page)
*T6: Read the value from memory address $1171 into the accumulator
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