AMD Am186 Series, Instruction Set, Page: 205 / 320

Instruction Set 4-165
NOP No Operation NOP
What It Does
NOP expends clock cycles exchanging AX with itself.
Syntax
Description
NOP performs no operation. It is a 1-byte instruction that takes up space in the code
segment, but affects none of the machine context except the instruction pointer.
Operation It Performs
Flag Settings After Instruction
Examples
This example shows a delay loop.
Form Opcode Description
Clocks
Am186 Am188
NOP 90 Perform no operation 3 3
NOP
/* exchange AX with AX to pass time */
temp = AX;
AX = AX;
AX = temp;
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Processor Status
Flags Register
reserved
OF DF IF TF SF ZF AF PF CF
? = undefined; – = unchanged
– – – – – – res – res – res –
; perform delay loop to insert real-time
MOV AX,0FFFFh; set up counter
LOOP1:
; waste time
NOP
NOP
NOP
NOP
DEC AX ; subtract 1 from counter
JNZ LOOP1 ; if AX is not 0, jump to top of loop