ATtiny261A datasheet(101/292 Pages) ATMEL

101 / 292 page

101

8197A–AVR–10/09

ATtiny261A/461A/861A

Figure 12-13. Phase and Frequency Correct PWM Mode, Timing Diagram

The Timer/Counter Overflow Flag (TOV1) 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 OC1x pins. Setting the COM1x1:0 bits to two will produce a non-inverted

PWM and setting the COM1x1:0 to three will produce an inverted PWM output. Setting the

COM1A1:0 bits to one will enable complementary Compare Output mode and produce both the

non-inverted (OC1x) and inverted output (OC1x). 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 (OCW1x) at the Compare Match between OCR1x and

TCNT1 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:

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

the TOP value.

The extreme values for the OCR1C Register represent special cases when generating a PWM

waveform output in the Phase and Frequency Correct PWM mode. If the OCR1C is set equal to

BOTTOM, the output will be continuously low and if set equal to MAX the output will be continu-

ously high for non-inverted PWM mode. For inverted PWM the output will have the opposite

logic values.

The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from

the Dead Time Generator, if either of the COM1x1:0 bits are set and the Data Direction Register

bits for the OC1X and OC1X pins are set as an output. If the COM1x1:0 bits are cleared, the

TOVn Interrupt Flag Set

OCnx Interrupt Flag Set

TCNTn

Period

OCWnx

(COMnx = 2)

(COMnx = 3)

OCRnx Update

fOCnxPCPWM

fclkT1

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