ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 127

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

16.9.4
9223B–AVR–09/11
Phase Correct PWM Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGM13:0 = 1, 2, 3,
10, or 11) provides a high resolution phase correct PWM waveform generation option. The
phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a
dual-slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and
then from TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare
(OC1x) is cleared on the compare match between TCNT1 and OCR1x while upcounting, and
set on the compare match while downcounting. In inverting Output Compare mode, the opera-
tion 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.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or
defined by either ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A
set to 0x0003), and the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM
resolution in bits can be calculated by using the following equation:
In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGM13:0 = 1, 2, or 3), the value in ICR1
(WGM13:0 = 10), or the value in OCR1A (WGM13:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNT1 value will be equal to TOP for one timer
clock cycle. The timing diagram for the phase correct PWM mode is shown on
The figure shows phase correct PWM mode when OCR1A or ICR1 is used to define TOP. The
TCNT1 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 TCNT1 slopes represent compare matches between OCR1x and TCNT1.
The OC1x Interrupt Flag will be set when a compare match occurs.
Figure 16-8. Phase Correct PWM Mode, Timing Diagram
R
PCPWM
TCNTn
OCnx
OCnx
Period
Atmel ATmega48PA/88PA/168PA [Preliminary]
=
log
---------------------------------- -
log
TOP
2
+
1
1
2
3
4
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
TOVn Interrupt Flag Set
(Interrupt on Bottom)
(COMnx1:0 = 2)
(COMnx1:0 = 3)
Figure
16-8.
127