Can you explain the principle of operation of ISR (Interrupt Service Routine)?

ISR (Interrupt Service Routine) is a function or procedure that is called in response to a hardware or software interrupt. When an event occurs that requires immediate attention from the processor (for example, a signal from an input device), the hardware generates an interrupt, and control is transferred to the ISR.

Key points of ISR operation:

• ISR quickly handles the event to minimize system lock-up time.
• Usually, ISR executes with a higher priority than the main code.
• Long operations or blocking code should not be performed in ISR.
• After handling the interrupt, ISR returns control to the main program.

Example: when a button is pressed, the microcontroller calls the ISR, which immediately records the fact of the press, and the main program then processes this event.