What are NOP and HLT instructions ?
NOP Instruction :
Mnemonic NOP Flags : It does not affect any flag.
NOP : No operation
Algorithm Do nothing
Addr. mode Implied addressing mode
Operation The execution of this instruction causes the CPU to do nothing.
- This instruction causes the CPU to do nothing. This instruction uses three clock cycles and increments the instruction pointer to point to the next instruction.
- It can be used to increase the delay of a delay loop.
Example :
MOV AL, 00011011b
NOT AL ; AL = 11100100b
RET
Flags : All unchanged.
HLT (Halt until interrupt or reset) Instruction :
Mnemonic Halt processing Flags : No flags are affected.
Operation :
- The HLT instruction will cause the 8086 to stop fetching and executing instructions. The 8086 enters into a half state. To come out of the halt state, there are 3 ways : (a) Interrupt signal on INTR pin, (b) Interrupt signal on NMI pin, (c) Reset signal on reset pin.
- It may be used as an alternative to an endless software loop in situations where a program must wait for an interrupt.
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