Two AVR-GCC examples of using AVR 8 bit Timers
Timers are very important part of microcontrollers. They can can be used in many areas starting with simple timed routines to RTOS. Good thing is that timers run independently to main program flow. Set up the timer counter and let it do its job while your main program runs and does its job.
Lets take AVR Atmega8 microcontroller. It has two independent 8 bit timers. One is little simpler which is featured with basic functions like:
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Single channel counter;
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Frequency generator;
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External Event counter;
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10 – bit clock pre-scaler.
Another is more advanced where is OCR (output compare register) included, which allows to implement PWM routines. It has following features:
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Single Channel Counter
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Clear Timer on Compare Match (Auto Reload)
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Glitch-free, phase Correct Pulse Width Modulator (PWM)
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Frequency Generator
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10-bit Clock Pre-scaler
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Overflow and Compare Match Interrupt Sources (TOV2 and OCF2)
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Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
Datasheet documents these timers pretty well.
Lets view couple examples with both 8 bit timers.
First example is to do simple task – every time timer overflows it has to increase variable value by one. And this variable is sent to PORTB in forever loop.
AVR-GCC code:
Another example is for second 8 bit timer. Code example shows phase correct PWM routine:
Added screen shot of simulation with VMLAB:
Second simulation files You may download here Timer2.
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