📖 7. Interrupt Instructions of 8085

📖 From An Introduction To Microprocessor 8085 • 185 questions available

About 7. Interrupt Instructions of 8085

Imagine you are reading a book (executing your main program), but a fire alarm goes off—you must stop reading immediately, check what’s happening, and then decide to continue. An interrupt is exactly that "fire alarm" for a microprocessor. It is a signal from an external device (like a keyboard or a timer) that tells the processor to pause its current job, attend to the device's urgent needs, and then resume the main program. This chapter covers the 8085's hardware pins that enable this capability.

How It Works: The 8085 has five interrupt pins: TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. They have a priority order (TRAP is the highest and non-maskable, meaning it can't be ignored—like a power failure). When an interrupt occurs, the CPU finishes its current instruction, saves the return address on the stack, and jumps to a predefined memory location (called an interrupt vector) to run a special "Interrupt Service Routine" (ISR). After the ISR is done, the RET instruction brings it back to the main program. This allows the CPU to handle real-time events efficiently.

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🔄 Last updated: 2026-07-30