Rainbow Electronics ATtiny861_V - Manual (Page 104)

104
2588B–AVR–11/06
ATtiny261/461/861
16.7.3 Phase and Frequency Correct PWM Mode
The Phase and Frequency Correct PWM Mode (PWMx = 1 and WGM10 = 1) provides a high
resolution Phase and Frequency Correct PWM waveform generation option. The Phase and
Frequency Correct PWM mode is based on a dual-slope operation. The counter counts repeat-
edly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM. In non-
inverting Compare Output Mode the Waveform Output (OCW1x) is cleared on the Compare
Match between TCNT1 and OCR1x while upcounting, and set on the Compare Match while
down-counting. In inverting Output Compare mode, the operation is inverted. In complementary
Compare Output Mode, the Waveform Ouput is cleared on the Compare Match and set at BOT-
TOM. 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 timing diagram for the Phase and Frequency Correct PWM mode is shown on Figure 16-12
in which the TCNT1 value is shown as a histogram for illustrating the dual-slope operation. The
counter is incremented until the counter value matches TOP. When the counter reaches TOP, it
changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle.
The diagram includes the Waveform Output (OCW1x) in non-inverted and inverted Compare
Output Mode. The small horizontal line marks on the TCNT1 slopes represent Compare
Matches between OCR1x and TCNT1.
Figure 16-12. Phase and Frequency Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV1) 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.
Table 16-3. Output Compare Pin Configurations in Fast PWM Mode
COM1x1 COM1x0 OC1x Pin OC1x Pin
0 0 Disconnected Disconnected
0 1 OC1x OC1x
1 0 Disconnected OC1x
1 1 Disconnected OC1x
TOVn Interrupt Flag Set
OCnx Interrupt Flag Set
1 2 3
TCNTn
Period
OCWnx
OCWnx
(COMnx = 2)
(COMnx = 3)
OCRnx Update