Datasheet

75
2466T–AVR–07/10
ATmega16(L)
Figure 30. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the Output Compare (OC0) from the Waveform
Generator if either of the COM01:0 bits are set. However, the OC0 pin direction (input or output)
is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Regis-
ter bit for the OC0 pin (DDR_OC0) must be set as output before the OC0 value is visible on the
pin. The port override function is independent of the Waveform Generation mode.
The design of the output compare pin logic allows initialization of the OC0 state before the out-
put is enabled. Note that some COM01:0 bit settings are reserved for certain modes of
operation. See “8-bit Timer/Counter Register Description” on page 83.
Compare Output Mode
and Waveform
Generation
The Waveform Generator uses the COM01:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COM01:0 = 0 tells the waveform generator that no action on the OC0
Register is to be performed on the next compare match. For compare output actions in the non-
PWM modes refer to Table 39 on page 84. For fast PWM mode, refer to Table 40 on page 84,
and for phase correct PWM refer to Table 41 on page 84.
A change of the COM01:0 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
FOC0 strobe bits.
PORT
DDR
DQ
DQ
OCn
Pin
OCn
DQ
Waveform
Generator
COMn1
COMn0
0
1
DATA B US
FOCn
clk
I/O