Datasheet

8183F–AVR–06/12

ATtiny24A/44A/84A

Figure 12-5. Compare Match Output Unit, Schematic (non-PWM Mode)

The general I/O port function is overridden by the Output Compare (OC1x) from the Waveform

Generator if either of the COM1x[1:0] bits are set. However, the OC1x pin direction (input or out-

put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction

ble on the pin. The port override function is generally independent of the Waveform Generation

mode, but there are some exceptions. See Table 12-2 on page 107, Table 12-3 on page 107

and Table 12-4 on page 107 for details.

The design of the Output Compare pin logic allows initialization of the OC1x state before the out-

put is enabled. Note that some COM1x[1:0] bit settings are reserved for certain modes of

operation. See “Register Description” on page 106

The COM1x[1:0] bits have no effect on the Input Capture unit.

12.7.1 Compare Output Mode and Waveform Generation

The Waveform Generator uses the COM1x[1:0] bits differently in normal, CTC, and PWM

modes. For all modes, setting the COM1x[1:0] = 0 tells the Waveform Generator that no action

on the OC1x Register is to be performed on the next compare match. For compare output

actions in the non-PWM modes refer to Table 12-2 on page 107. For fast PWM mode refer to

Table 12-3 on page 107, and for phase correct and phase and frequency correct PWM refer to

Table 12-4 on page 107.

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 1x strobe bits.

PORT

DDR

OCnx

Waveform

Generator

COMnx1

COMnx0

DATA BU

FOCnx

clk

I/O