ATmega162 datasheet(125/324 Pages) ATMEL

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2513K–AVR–07/09

ATmega162/V

Using the ICRn Register for defining TOP works well when using fixed TOP values. By using

ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,

if the base PWM frequency is actively changed by changing the TOP value, using the OCRnA as

TOP is clearly a better choice due to its double buffer feature.

In phase and frequency correct PWM mode, the compare units allow generation of PWM wave-

forms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and

an inverted PWM output can be generated by setting the COMnx1:0 to three (See Table 55 on

page 129). The actual OCnx value will only be visible on the port pin if the data direction for the

port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing)

the OCnx Register at the Compare Match between OCRnx and TCNTn when the counter incre-

ments, and clearing (or setting) the OCnx Register at Compare Match between OCRnx and

TCNTn when the counter decrements. The PWM frequency for the output when using phase

and frequency correct PWM can be calculated by the following equation:

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). For Timer/Counter3 also

prescaler factors 16 and 32 are available.

The extreme values for the OCRnx Register represents special cases when generating a PWM

waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM the

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

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

is used to define the TOP value (WGMn3:0 = 9) and COMnA1:0 = 1, the OCnA output will toggle

with a 50% duty cycle.

fOCnxPFCPWM

clk_I/O

NTOP

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ATmega162 датащи(PDF) 125 Page - ATMEL Corporation