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My Notes On The Atmel 8-bit AVR ATmega168 Microcontroller

Interrupts And Timers	How to Control 30 LEDS With Only 6 Pins
Create Sounds Using A PC Speaker

Timers And Interrupts On The ATMEGA168 Microcontroller

There are three timers available to you on the ATmega168. There is one 16-bit timer, called Counter 1 and two 8-bit timers called Counter 0 and Counter 2. The 16-bit timer can count up from 0 to 65,535 (Which in Binary is 11111111 11111111). The 8-bit timers can only count up from 0 to 255 (Which in Binary is 11111111).

How To Setup The 8-bit Timers	How To Setup The 16-bit Timers
Now For the Software End Of Things	Timer Counting Speed Table
8-bit Timer Example - Use Software To Control A LED	16-bit Timer Example - Use Software To Control A LED
8-bit Timer Example - Use Hardware To Control A LED	16-bit Timer Example 2 - Use Software To Control A LED
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Timer Counting Speed Table

How fast should the timer count, in relation to the clock speed of the microcontroller (Typically 8 MHz / 20 MHz)

Values for an 8 MHz clock

Prescaler	Duration of one timer tick	Frequency (timer ticks per second)	Time until overflow 16-bit	Time until overflow 8-bit
CLOCK_DIV_1	0.125 us ( 1 / 8000000 sec)	8000.0000 kHz (8000000 / 1 Hz)	8.192 ms	0.032ms
CLOCK_DIV_8	1.000 us ( 8 / 8000000 sec)	1000.0000 kHz (8000000 / 8 Hz)	65.536 ms	0.256ms
CLOCK_DIV_64	8.000 us ( 64 / 8000000 sec)	125.0000 kHz (8000000 / 64 Hz)	524.288 ms	2.048ms
CLOCK_DIV_256	32.000 us ( 256 / 8000000 sec)	31.2500 kHz (8000000 / 256 Hz)	2097.152 ms	8.192ms
CLOCK_DIV_1024	128.000 us (1024 / 8000000 sec)	7.8125 kHz (8000000 / 1024 Hz)	8388.608 ms	32.768ms

Values for a 20 MHz clock

Prescaler	Duration of one timer tick	Frequency (timer ticks per second)	Time until overflow 16-bit	Time until overflow 8-bit
CLOCK_DIV_1	0.05 us ( 1 / 20000000 sec)	20000.00000 kHz (20000000 / 1 Hz)	3.2768 ms	0.0128ms
CLOCK_DIV_8	0.40 us ( 8 / 20000000 sec)	2500.00000 kHz (20000000 / 8 Hz)	26.2144 ms	0.1024ms
CLOCK_DIV_64	3.20 us ( 64 / 20000000 sec)	312.50000 kHz (20000000 / 64 Hz)	209.7152 ms	0.8192ms
CLOCK_DIV_256	12.80 us ( 256 / 20000000 sec)	78.12500 kHz (20000000 / 256 Hz)	838.8608 ms	3.2768ms
CLOCK_DIV_1024	51.20 us (1024 / 20000000 sec)	19.53125 kHz (20000000 / 1024 Hz)	3355.4432 ms	13.1072ms

References