Design with Microprocessors (DMP) – Lab. 4 1

Beside external interrupt, the MCU responds to internal ones which are triggered by external events (on the external pins). The source of the internal interrupts are hardware components inside the MCU (like the Timers). Using the timer/counter interrupts, you can trigger events at specific time intervals (without using functions like delay and millis). Because these interrupts have an asynchronous behavior, the main program flow can be executed normally and only when a temporal threshold is reached a specific ISR is executed. The timer increments a counter register, and when its maximum counting capacity is reached an overflow bit (flag) is set. The flag can be manually checked or it can trigger an interrupt request. At the ISR execution the fag is reset. Each timer needs a clock source, which most commonly is the development board’s oscillator; its frequency can be divided by an auxiliary counter (prescaler)