Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
101
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
setting the COM0x1:0 to three: Setting the COM0A1:0 bits to one allows the OC0A pin to toggle on Compare
Matches if the WGM02 bit is set. This option is not available for the OC0B pin (see
Matches if the WGM02 bit is set. This option is not available for the OC0B pin (see
The actual OC0x value will only be visible on the port pin if the data direction for the port pin is set as output. The
PWM waveform is generated by setting (or clearing) the OC0x Register at the compare match between OCR0x
and TCNT0, and clearing (or setting) the OC0x Register at the timer clock cycle the counter is cleared (changes
from TOP to BOTTOM).
PWM waveform is generated by setting (or clearing) the OC0x Register at the compare match between OCR0x
and TCNT0, and clearing (or setting) the OC0x Register at the timer clock cycle the counter is cleared (changes
from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represents special cases when generating a PWM waveform
output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each
MAX+1 timer clock cycle. Setting the OCR0A equal to MAX will result in a constantly high or low output
(depending on the polarity of the output set by the COM0A1:0 bits.)
output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each
MAX+1 timer clock cycle. Setting the OCR0A equal to MAX will result in a constantly high or low output
(depending on the polarity of the output set by the COM0A1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to
toggle its logical level on each compare match (COM0x1:0 = 1). The waveform generated will have a maximum
frequency of f
toggle its logical level on each compare match (COM0x1:0 = 1). The waveform generated will have a maximum
frequency of f
OC0
= f
clk_I/O
/2 when OCR0A is set to zero. This feature is similar to the OC0A toggle in CTC mode,
except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
15.7.4 Phase Correct PWM Mode
The phase correct PWM mode (WGM02:0 = 1 or 5) provides a high resolution phase correct PWM waveform
generation option. The phase correct PWM mode is based on a dual-slope operation. The counter counts
repeatedly from BOTTOM to TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1,
and OCR0A when WGM2:0 = 5. In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared
on the compare match between TCNT0 and OCR0x while upcounting, and set on the compare match while
downcounting. In inverting Output Compare mode, the operation is inverted. The dual-slope operation has lower
maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-
slope PWM modes, these modes are preferred for motor control applications.
generation option. The phase correct PWM mode is based on a dual-slope operation. The counter counts
repeatedly from BOTTOM to TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1,
and OCR0A when WGM2:0 = 5. In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared
on the compare match between TCNT0 and OCR0x while upcounting, and set on the compare match while
downcounting. In inverting Output Compare mode, the operation is inverted. The dual-slope operation has lower
maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-
slope PWM modes, these modes are preferred for motor control applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the
counter reaches TOP, it changes the count direction. The TCNT0 value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on
counter reaches TOP, it changes the count direction. The TCNT0 value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on
. The TCNT0 value is in the
timing diagram shown as a histogram for illustrating the dual-slope operation. The diagram includes non-
inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare
matches between OCR0x and TCNT0.
inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare
matches between OCR0x and TCNT0.
f
OCnxPWM
f
clk_I/O
N 256
------------------
=