Rainbow Electronics ATtiny861_V User Manual

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106

2588B–AVR–11/06

ATtiny261/461/861

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 (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 single-
slope operation. The timing diagram includes Output Compare pins OC1A and OC1A, and the
corresponding Output Compare Override Enable bits (OC1OE1..OC1OE0).

Figure 16-13. PWM6 Mode, Single-slope Operation, Timing Diagram

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. The Output Compare pins can
also be overriden by the Output Compare Override Enable bits OC1OE5..OC1OE0. If an Over-
ride Enable bit is cleared, the actual value from the port register will be visible on the port pin

TCNT1

OC1A Pin

OC1B Pin

OC1D Pin

OC1OE0

OC1OE1

OC1OE2

OC1OE3

OC1OE4

OC1OE5

OCW1A