ATmega16U4 datasheet(153/408 Pages) ATMEL

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7766D–AVR–01/09

ATmega16U4/ATmega32U4

The Timer/Counter Overflow Flag (TOV4) is set each time the counter reaches TOP. If the inter-

rupt is enabled, the interrupt handler routine can be used for updating the compare value.4In

fast PWM mode, the compare unit allows generation of PWM waveforms on the OC4x pins. Set-

ting 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 COM4x1:0 bits to one will enable com-

plementary Compare Output mode and produce both the non-inverted (OC4x) and inverted

output (OC4x). The actual value 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 setting (or clearing) the Waveform

Output (OCW4x) at the Compare Match between OCR4x and TCNT4, and clearing (or setting)

the Waveform Output at the timer clock cycle the counter is cleared (changes from TOP to

BOTTOM).

The PWM frequency for the output can be calculated by the following equation:

The N variable represents the number of steps in single-slope operation. The value of N equals

either to the TOP value.

The extreme values for the OCR4C Register represents special cases when generating a PWM

waveform output in the fast PWM mode. If the OCR4C is set equal to BOTTOM, the output will

be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR4C equal to MAX will result

in a constantly high or low output (depending on the polarity of the output set by the COM4x1:0

bits.)

A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-

ting the Waveform Output (OCW4x) to toggle its logical level on each Compare Match

(COM4x1:0 = 1). The waveform generated will have a maximum frequency of f

OC4 = fclkT4/4 when

OCR4C is set to three.

The general I/O port function is overridden by the Output Compare value (OC4x / OC4x) from

the Dead Time Generator, if either of the COM4x1:0 bits are set and the Data Direction Register

bits for the OC4X and OC4X pins are set as an output. If the COM4x1:0 bits are cleared, the

actual value from the port register will be visible on the port pin. The Output Compare Pin config-

urations are described in Table 15-3.

15.8.3

Phase and Frequency Correct PWM Mode

The Phase and Frequency Correct PWM Mode (PWM4x = 1 and WGM40 = 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 OCR4C) and then from TOP to BOTTOM. In non-

inverting Compare Output Mode the Waveform Output (OCW4x) is cleared on the Compare

Table 15-3.

Output Compare Pin Configurations in Fast PWM Mode

COM4x1

COM4x0

OC4x Pin

Disconnected

01OC4x

OC4x

Disconnected

OC4x

Disconnected

OC4x

OCnxPWM

fclkT4

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