atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 172

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

172
ATmega32U4
Match between TCNT4 and OCR4x 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 Output 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
in which the TCNT4 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 TCNT4 value will be equal to TOP for one timer clock cycle.
The diagram includes the Waveform Output (OCW4x) in non-inverted and inverted Compare
Output Mode. The small horizontal line marks on the TCNT4 slopes represent Compare
Matches between OCR4x and TCNT4.
Figure 16-14. Phase and Frequency Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV4) 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.
In the Phase and Frequency Correct PWM mode, the compare unit allows generation of PWM
waveforms on the OC4x pins. Setting the COM4x1:0 bits to two will produce a non-inverted
PWM and setting the COM4x1:0 to three will produce an inverted PWM output. Setting the
COM4A1:0 bits to one will enable complementary Compare Output mode and produce both the
non-inverted (OC4x) and inverted output (OC4x). The actual values 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 Waveform Output (OCW4x) at the Compare Match between OCR4x and
TCNT4 when the counter increments, and setting (or clearing) the Waveform Output at Compare
Match when the counter decrements. The PWM frequency for the output when using the Phase
and Frequency Correct PWM can be calculated by the following equation:
TCNTn
OCWnx
(COMnx = 2)
OCWnx
(COMnx = 3)
Period
1
f
OCnxPCPWM
2
=
f
------------ -
clkT4
N
3
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
7766A–AVR–03/08
Figure 16-14