#At the end of every instruction, the IRQ (if the interrupt disable flag is clear) and NMI pins are checked.
For As an example, with let M[$42]=$80 and , M[$43]=$10 and Y=$F1, the . The instruction LDA ($42),Y will execute as follow, with phi2 as the first half-cycle and phi1 as the second half-cycle:
*T0: Fetch opcode $B1 (LDA (zp),Y) from memory then increment PC
*T1: Fetch operand byte $42 (zero page pointer address) then increment PC