________is the only non-maskable interrupt in 8085 microprocessor.

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TRAP

Explanation: TRAP is the only non-maskable interrupt (NMI) in the 8085 microprocessor. It cannot be disabled or ignored by the program and is used for critical tasks such as power failure or emergency shutdowns.

Working Principle: The TRAP interrupt is both edge and level triggered, meaning it requires a high level and a transition to stay active to be recognized. Being non-maskable, it bypasses the Interrupt Enable (INTE) flag and the mask settings of the SIM (Set Interrupt Mask) instruction, providing the highest priority among all hardware interrupts.

Key Formulas: $V_{trap} = 	ext{High Level transition}$ — The logic level requirement for TRAP triggering

Key Points: TRAP has the highest priority of all hardware interrupts in 8085.; It is both level and edge sensitive.; It cannot be masked by the SIM instruction.; Vector address of TRAP is $0024H$.

Advantages: Ensures critical routines are executed immediately regardless of current status.; Useful for emergency power-down procedures.

Disadvantages: Cannot be software-disabled, which may lead to conflicts if not managed correctly.

Applications: Emergency Power Failure Detection; Hardware Error Trapping; Real-time System Resets

Additional Info: RST 7.5, 6.5, and 5.5 are maskable interrupts and can be enabled/disabled using the EI/DI instructions and the SIM instruction.. INTR is the only non-vectored interrupt in 8085, requiring an external device to provide the interrupt vector/call instruction.

Answer: A is correct — TRAP is the only non-maskable interrupt in the 8085 microprocessor, ensuring execution regardless of the mask state.

Exam Tip: Always remember the priority order for 8085 interrupts: TRAP > RST 7.5 > RST 6.5 > RST 5.5 > INTR.

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