ata5773 ATMEL Corporation, ata5773 Datasheet - Page 128

• Manufacturer Part Number: ata5773
• Description: Microcontroller With Uhf Ask/fsk Transmitter
• Manufacturer: ATMEL Corporation

11.7.4
76
ATtiny24/44/84
Phase Correct PWM Mode
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 set-
ting OC0x to toggle its logical level on each Compare Match (COM0x1:0 = 1). The waveform
generated will have a maximum frequency of
ture 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.
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 BOT-
TOM. 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 down-
counting. 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 sym-
metric 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
illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM out-
puts. The small horizontal line marks on the TCNT0 slopes represent Compare Matches
between OCR0x and TCNT0.
Figure 11-7. Phase Correct PWM Mode, Timing Diagram
TCNTn
OCn
OCn
Period
Figure 11-7 on page
76. The TCNT0 value is in the timing diagram shown as a histogram for
1
2
0
= f
clk_I/O
/2 when OCR0A is set to zero. This fea-
3
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
(COMnx1:0 = 2)
(COMnx1:0 = 3)
8006G–AVR–01/08