ATtiny261A datasheet(102/292 Pages) ATMEL

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102

8197A–AVR–10/09

ATtiny261A/461A/861A

actual value from the port register will be visible on the port pin. The configurations of the Output

Compare Pins are described in Table 12-4.

12.8.4

PWM6 Mode

The PWM6 Mode (PWM1A = 1, WGM11:10 = 1X) provide PWM waveform generation option

e.g. for controlling Brushless DC (BLDC) motors. In the PWM6 Mode the OCR1A Register con-

trols all six Output Compare waveforms as the same Waveform Output (OCW1A) from the

Waform Generator is used for generating all waveforms. The PWM6 Mode also provides an Out-

put 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 Waveforn Output (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 BOTTOM). 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 compare 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 Waveforn 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 when the COM1A1:0 bits are

set to “10” is shown in Figure 12-14. 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 single-slope operation. The tim-

ing diagram includes Output Compare pins OC1A and OC1A, and the corresponding Output

Compare Override Enable bits (OC1OE1:OC1OE0).

Table 12-4.

Output Compare pin configurations in Phase and Frequency Correct PWM Mode

COM1x1

COM1x0

OC1x Pin

Disconnected

OC1x

Disconnected

OC1x

Disconnected

OC1x

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