ATmega16 datasheet(80/357 Pages) ATMEL

80 / 357 page

2466S–AVR–05/09

ATmega16(L)

PWM frequency for the output when using phase correct PWM can be calculated by the follow-

ing equation:

The N variable represents the prescale factor (1, 8, 64, 256, or 1024).

The extreme values for the OCR0 Register represent special cases when generating a PWM

waveform output in the phase correct PWM mode. If the OCR0 is set equal to BOTTOM, the out-

put will be continuously low and if set equal to MAX the output will be continuously high for non-

inverted PWM mode. For inverted PWM the output will have the opposite logic values.

At the very start of Period 2 in Figure 33 OCn has a transition from high to low even though there

is no Compare Match. The point of this transition is to guarantee symmetry around BOTTOM.

There are two cases that give a transition without Compare Match:

•

OCR0A changes its value from MAX, like in Figure 33. When the OCR0A value is MAX the

OCn pin value is the same as the result of a down-counting Compare Match. To ensure

symmetry around BOTTOM the OCn value at MAX must be correspond to the result of an

up-counting Compare Match.

•

The Timer starts counting from a value higher than the one in OCR0A, and for that reason

misses the Compare Match and hence the OCn change that would have happened on the

way up.

fOCnPCPWM

clk_I/O

N 510

⋅

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ATmega16 Datasheet(PDF) 80 Page - ATMEL Corporation