What Is Timer Interrupt?


Author: Roslyn
Published: 1 Mar 2022

PORTA: A program to detect the timer from an interrupt

The diagram of the project is shown in Figure 6.2. The circuit is the same as in Figure 5.56, but the external input interrupt is used for event triggering. The display digits are cleared and the register T0CON is loaded with 0xC5 to enable the TMR0 and set the prescaler to 64.

The TMR0L register has 100 loaded so that an interrupt can be generated every 5 ms. The rest of the main program is waiting for an interrupt to happen and does not do anything. The program checks to see if the interrupt is from the same source.

If the timer has caused an interrupt, the timer register is reloaded and the timer interrupt flag is cleared so that the processor can accept more interrupt from the timer. The display digits are refreshed inside the timer. Only one digit is enabled here.

Each interrupt, data is sent to the digit that is enabled. The local APIC has the next category of timer. The local timer can be programmed to send a local interrupt to the associated processor when a count is reached.

When the count reaches zero, the current-count register is reloaded from the initial register, and the count is repeated. If the initial-count register is set, counting will restart using the new initial-count value. The initial-count register is read-only, while the current-count register is read only.


Timers are simple counters that count at a certain Frequency. You can change the clock divisor to make it work better. You can also change the time period to a specific count.


An interrupt is a computer signal that tells the computer to stop running the current program so that a new one can be started or a circuit that carries such a signal. An interrupt is a signal to stop Microsoft Word so that a PowerPoint presentation can start. A signal is sent to the computer's processor by a hardware device.

Timer Interrupt and Preemption

If you check to see if the process quantum has expired, you might say the scheduler is likely to run on every timer interval. Interrupt handlers need to be short for the purpose of stacking. Many operating systems schedule events to be delivered.

Windoze is a software driven interrupt system. The process can be delivered with the timer interrupt. DPC is not related to scheduler because it is the job of the processor to decide what to run next on the computer.

The technique of timer interruption is related to the technique of preemption. A timer may be set to a specific interval when a process gets the most powerful machine. The process is still using the processor at the end of the interval.

A note on the timer1 in CTC mode

The first example uses the timer1 in the CTC mode to set a light. The timer is set to a Frequency of 2Hz. The interrupt service routine has the toggled the light up indicator.

Periodic Timers for Real-Time Operating Systems

Periodic timers are useful for pacing events, creating delays, and serving as a heartbeat for real-time operating systems. The next article in the series covers a timer that uses pulse width modulation to give a flexible interface to the outside world.

General-Purpose Timers

The two general-purpose timers are functionally identical. Timer0 and Timer1. The timers and Prescaler are 32-bit.

A timer allows us to time things. The Timer module can be used as a counter or timer. Interrupt Register has flag bits for match interrupt and capture interrupt.

Four bits are used for match and capture interrupt. Match Register Interrupts are defined as bits 0 to 3 in the IR register. The bits 4 to 7 are for Capture Register Interrupts.

The corresponding bit in the IR register is set if an interrupt is triggered. The counter is used to calculate the value of the PR. The PC is reset when the value in the PC is equal to the value in the PR.

If PR is 2, then the peripheral clock's clock rate is incremented every third cycle. The resolution of the Timer is defined by PC. The Timer Counter value is compared to the Match register values.

Interrupts: Input Handler for Fire

They are called this because they will interrupt the thread of execution after the current instruction is completed and run their code, returning to where they left off when it was over. Interrupts are used to create input handlers that can fire when an event occurs, even if it is not in your code.

The prescaler

The prescaler can be used to reduce a counter to a lower one. The timer clock is taken by the prescaler and divided into different values before feeding it.

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