⚙️ External Interrupt Interface — Register-Level (Arduino UNO)

This project demonstrates how to configure and handle external interrupts (INT0 & INT1) on the ATmega328P at the register level, without using Arduino functions.

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⚙️ Hardware Used

• Arduino UNO (ATmega328P)
• 2 Push Buttons (for INT0 & INT1)
• LED (on pin 13, PB5)
• 10kΩ Pull-down or Pull-up Resistors (if needed)

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🔌 Pin Configuration

Component	Function	Arduino Pin	Port
Push Button 1	External Interrupt 0	D2	PD2 / INT0
Push Button 2	External Interrupt 1	D3	PD3 / INT1
LED	Output	D13	PB5
VCC	Power	+5V	—
GND	Ground	GND	—

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🧩 Code Explanation

Key Registers Used

Register	Purpose
DDRB	Configure PB5 as output
SREG	Global Interrupt Enable (bit 7)
EIMSK	Enable specific external interrupts (INT0, INT1)
EICRA	Set interrupt trigger edge (rising, falling, etc.)

Logic

• INT0 (D2) → When pressed, triggers ISR → LED ON
• INT1 (D3) → When pressed, triggers ISR → LED OFF

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⚙️ Working Principle

1. Button 1 (INT0) sends a rising edge → LED turns ON.
2. Button 2 (INT1) sends a rising edge → LED turns OFF.
3. The CPU sleeps in the main loop until an interrupt occurs.

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🧰 Build & Upload

1. Compile with AVR-GCC / Atmel Studio / PlatformIO.
2. Upload the HEX to Arduino UNO.
3. Observe LED toggling as external interrupts occur.