ATmega16U4 datasheet(154/408 Pages) ATMEL

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7766D–AVR–01/09

ATmega16U4/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 Figure 15-14

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 15-14. 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:

TOVn Interrupt Flag Set

OCnx Interrupt Flag Set

TCNTn

Period

OCWnx

(COMnx = 2)

(COMnx = 3)

OCRnx Update

OCnxPCPWM

clkT4

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