O D I T S Z A P C OF: Overflow flag TF: Trap flag AF: Aux carry F F F F F F F F F DF: Direction flag SF: Sign flag PF: Parity flag <none> IF: Interrupt flag ZF: Zero flag CF: Carry flag
NOP <none>
NOP
This, the easiest-to-understand of all 86-family machine instructions, simply does nothing. Its job is to take up space in sequences of instructions. When fetched by the CPU, NOP is executed as XCHG AX,AX. So, some work is actually done, but it's not useful work, and no data is altered anywhere. The flags are not affected. NOP is used for "NOPping out" machine instructions during debugging, leaving space for future procedure or interrupt calls, or padding timing loops.
r8 = AL AH BL BH CL CH DL DH r16 = AX BX CX DX BP SP SI DI sr = CS DS SS ES FS GS r32 = EAX EBX ECX EDX EBP ESP ESI EDI m8 = 8-bit memory data m16 = 16-bit memory data m32 = 32-bit memory data i8 = 8-bit immediate data i16 = 16-bit immediate data i32 = 32-bit immediate data d8 = 8-bit signed displacement d16 = 16-bit signed displacement d32 = 32-bit unsigned displacement