Datasheet

98
8197C–AVR–05/11
ATtiny261A/461A/861A
The design of the Output Compare Pin Configuration logic allows initialization of the OC1x state
before the output is enabled. Note that some COM1x[1:0] bit settings are reserved for certain
modes of operation. For Output Compare Pin Configurations refer to Table 12-2 on page 99,
Table 12-3 on page 101, Table 12-4 on page 103, Table 12-5 on page 104, Table 12-6 on page
104, and Table 12-7 on page 105.
12.7.1 Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM1x[1:0] bits differently in Normal mode and PWM
modes. For all modes, setting the COM1x[1:0] = 0 tells the Waveform Generator that no action
on the OCW1x Output is to be performed on the next Compare Match. For compare output
actions in the non-PWM modes refer to Table 12-8 on page 111. For fast PWM mode, refer to
Table 12-9 on page 111, and for the Phase and Frequency Correct PWM refer to Table 12-10 on
page 112. A change of the COM1x[1:0] bits state will have effect at the first Compare Match
after the bits are written. For non-PWM modes, the action can be forced to have immediate
effect by using the FOC1x strobe bits.
12.8 Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of waveform generation mode bits (PWM1A, PWM1B, and
WGM1[1:0]) and compare output mode bits (COM1x[1:0]). The Compare Output mode bits do
not affect the counting sequence, while the Waveform Generation mode bits do. The
COM1x[1:0] bits control whether the PWM output generated should be inverted, non-inverted or
complementary. For non-PWM modes the COM1x[1:0] bits control whether the output should be
set, cleared, or toggled at a Compare Match.
12.8.1 Normal Mode
The simplest mode of operation is Normal mode (PWM1A/PWM1B = 0), where the counter
counts from BOTTOM to TOP (defined as OCR1C) then restarts from BOTTOM. The OCR1C
defines the TOP value for the counter, hence also its resolution, and allows control of the Com-
pare Match output frequency. In toggle Compare Output Mode the Waveform Output (OCW1x)
is toggled at Compare Match between TCNT1 and OCR1x. In non-inverting Compare Output
Mode the Waveform Output is cleared on the Compare Match. In inverting Compare Output
Mode the Waveform Output is set on Compare Match. The timing diagram for Normal mode is
shown in Figure 12-11.
Figure 12-11. Normal Mode, Timing Diagram
TCNTn
OCWnx
(COMnx=1)
OCnx Interrupt Flag Set
1 4
Period
2 3
TOVn Interrupt Flag Set