ATtiny261-ESSZ datasheet(107/227 Pages) ATMEL

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107

7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

16.7.4

PWM6 Mode

The PWM6 Mode (PWM1A = 1, WGM11 = 1 and WGM10 = x) provide PWM waveform genera-

tion option e.g. for controlling Brushless DC (BLDC) motors. In the PWM6 Mode the OCR1A

from the Waveform Generator is used for generating all waveforms. The PWM6 Mode also pro-

vides an Output Compare Override Enable Register (OC1OE) that can be used with an instant

response for disabling or enabling the Output Compare pins. If the Output Compare Override

Enable bit is cleared, the actual value from the port register will be visible on the port pin.

The PWM6 Mode provides two counter operation modes, a single-slope operation and a

dual-slope operation. If the single-slope operation is selected (the WGM10 bit is set to 0), the

counter counts from BOTTOM to TOP (defined as OCR1C) then restart from BOTTOM like in

Fast PWM Mode. The PWM waveform is generated by setting (or clearing) the Waveform Out-

put (OCW1A) at the Compare Match between OCR1A and TCNT1, and clearing (or setting) the

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

TOM). The Timer/Counter Overflow Flag (TOV1) is set each time the counter reaches the TOP

and, if the interrupt is enabled, the interrupt handler routine can be used for updating the com-

pare value.

Whereas, if the dual-slope operation is selected (the WGM10 bit is set to 1), the counter counts

repeatedly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM like in

Phase and Frequency Correct PWM Mode. The PWM waveform is generated by setting (or

clearing) the Waveform Output (OCW1A) at the Compare Match between OCR1A and TCNT1

when the counter increments, and clearing (or setting) the Waveform Output at the he Compare

Match between OCR1A and TCNT1 when the counter decrements. The Timer/Counter Overflow

Flag (TOV1) is set each time the counter reaches the BOTTOM and, if the interrupt is enabled,

the interrupt handler routine can be used for updating the compare value.

The timing diagram for the PWM6 Mode in single-slope operation (WGM11 = 0) when the

COM1A1:0 bits are set to “10” is shown in Figure 16-13. The counter is incremented until the

counter value matches the TOP value. The counter is then cleared at the following timer clock

cycle. The TCNT1 value is in the timing diagram shown as a histogram for illustrating the sin-

gle-slope operation. The timing diagram includes Output Compare pins OC1A and OC1A, and

the corresponding Output Compare Override Enable bits (OC1OE1..OC1OE0).

Table 16-4.

Output Compare pin configurations in Phase and Frequency Correct PWM Mode

COM1x1

COM1x0

OC1x Pin

Disconnected

01OC1x

OC1x

Disconnected

OC1x

Disconnected

OC1x

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