ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 79

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

7701E–AVR–02/11
This high frequency makes the fast PWM mode well suited for power regulation, rectification,
and DAC applications. High frequency allows the use of physically smaller external compo-
nents (coils, capacitors, etc.), and hence reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in
shown as a histogram for illustrating the single-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.
Figure 13-6. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the
interrupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast 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, and an inverted PWM out-
put can be generated by setting the COM0x1:0 bits to three. Setting the COM0A1:0 bits to one
allows the AC0A pin to toggle on compare matches if the WGM02 bit is set. This option is not
available for the OC0B pin (See
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 when the coun-
ter is cleared (changes from top to bottom).
The PWM frequency for the output can be calculated by the following equation:
The variable N represents the prescale factor (1, 8, 64, 256, or 1024)..
f
OCnxPWM
TCNTn
OCn
OCn
Period
=
-------------------- -
N
f
clk_I/O
1
256
Figure 13-6 on page
2
Atmel ATtiny24/44/84 [Preliminary]
3
Table 13-3 on page
4
79. The TCNT0 value is in the timing diagram
5
84). The actual OC0x value will only be
6
7
OCRnx Interrupt Flag Set
OCRnx Update and
TOVn Interrupt Flag Set
(COMnx1:0 = 2)
(COMnx1:0 = 3)
79