IAR For AVR timer interrupt initial value calculation method-EEWORLD

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Using chip AT Mega16 external crystal oscillator 4.00MHz

Timer 1 (16-bit timer) register TCCR1B = 0x04 Set 256 prescaler

To use the timer for 1 second

1, 4000000 / 256 = 15625 means the timer will trigger an interrupt every 1/15625 seconds

2, 65535 - 15625 = 49910 Calculate how many times to accumulate to trigger the overflow interrupt of timer 1 after 1 second

3, 49910 <==> C2 F6 Convert the calculated value into hexadecimal

4, TCNT1H = 0xC2; Assign register
TCNT1L = 0xF6;

================================================== ===========================

For example, using 16-bit timer TIMER1, 4MHZ crystal, 256 division, 100ms timing, how to get the initial value to assign to TCNT1?

65536-(4M/256)*0.1=63973.5

Among them, 4M is the crystal frequency, and 0.1 is the timing duration in seconds.

For an 8-bit timer,
T = (2^8-counting initial value) * crystal period * frequency division = (2^8-counting initial value) / crystal frequency * frequency division
Counting initial value = 2^8-T / crystal period / frequency division = 2^8-T * crystal frequency / frequency division

Because AVR one instruction one cycle

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