NOP, HLT, DI, EI, RIM, SIM

1.NOP(No operation): - No operation is performed. The instruction is fetched and decoded. However no operation is executed.

Eg: - NOP

2. HLT(Halt): - The CPU finishes executing the current instruction and halts any further
execution. An interrupt or reset is necessary to exit from the halt state.

Eg: - HLT

3. DI(Disable Interrupt): - The interrupt enable flip-flop is reset and all the interrupts except the TRAP are disabled. No flags are affected.

Eg: - DI

4. EI(Enable Interrupt): - The interrupt enable flip-flop is set and all interrupts are enabled. No flags are affected. After a system reset or the acknowledgement of an interrupt, the interrupt enable flipflop is reset, thus disabling the interrupts. This instruction is necessary to reenable the interrupts (except TRAP).

Eg: - EI

5. RIM(Read interrupt mas): - This is a multipurpose instruction used to read the status of interrupts 7.5, 6.5, 5.5 and read serial data input bit. The instruction loads eight bits in the accumulator with the following interpretations.

Eg: - RIM

6.SIM(Set interrupt mask)