Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
102
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Figure 15-7.
Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The Interrupt Flag
can be used to generate an interrupt each time the counter reaches the BOTTOM value.
can be used to generate an interrupt each time the counter reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting
the COM0x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by
setting the COM0x1:0 to three: Setting the COM0A0 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
the COM0x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by
setting the COM0x1:0 to three: Setting the COM0A0 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
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 clearing (or setting) the OC0x Register at the compare match between OCR0x
and TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at compare match
between OCR0x and TCNT0 when the counter decrements. The PWM frequency for the output when using
phase correct PWM can be calculated by the following equation:
PWM waveform is generated by clearing (or setting) the OC0x Register at the compare match between OCR0x
and TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at compare match
between OCR0x and TCNT0 when the counter decrements. The PWM frequency for the output when using
phase correct PWM 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 represent special cases when generating a PWM waveform output
in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, the output 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.
in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, the output 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
OCnx 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.
that give a transition without Compare Match.
OCRnx changes its value from MAX, like in
. 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 OCnx value at MAX must correspond to the result of an up-counting Compare Match.
BOTTOM the OCnx value at MAX must correspond to the result of an up-counting Compare Match.
The timer starts counting from a value higher than the one in OCRnx, and for that reason misses the
Compare Match and hence the OCnx change that would have happened on the way up.
Compare Match and hence the OCnx change that would have happened on the way up.
TOVn Interrupt Flag Set
OCnx Interrupt Flag Set
1
2
3
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx Update
f
OCnxPCPWM
f
clk_I/O
N 510
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