With 8 MHz E clock, basic time unit T is 0.125 s.
Prescaler changes time unit for timer module (input capture, output compare, timer overflow) to prescaler.
For example, PR2:0 = 011 => prescaler = 8, so TCNT is incremented every 1 s.
When reading input capture, elapsed time = prescaler T.
For example, PR2:0 = 011 and TC2 - TC1 = 12,500, then
elapsed time = ms
Want OC to do something after time X seconds, what to add to TCx?
For example, to create 1 kHz square wave, half-period is 500 s. If prescaler is 8, then add:
and TCx = TCx + 500
For example, to have pulse width modulation on OC1 with 500 Hz frequency and 80% duty cycle, with prescaler = 2:
=> 2 ms, so add to TC7:
For 80% duty cycle, add to TC1.