Datasheet

compare match will be missed, resulting in incorrect waveform generation. Similarly, do not write the

TCNT2 value equal to BOTTOM when the counter is downcounting.

The setup of the OC2x should be performed before setting the Data Direction Register for the port pin to

output. The easiest way of setting the OC2x value is to use the Force Output Compare (FOC2x) strobe bit

in Normal mode. The OC2x Register keeps its value even when changing between Waveform Generation

modes.

Be aware that the COM2x[1:0] bits are not double buffered together with the compare value. Changing

the COM2x[1:0] bits will take effect immediately.

19.6. Compare Match Output Unit

The Compare Output mode (COM2x[1:0]) bits have two functions. The Waveform Generator uses the

COM2x[1:0] bits for defining the Output Compare (OC2x) state at the next compare match. Also, the

COM2x[1:0] bits control the OC2x pin output source. The following figure shows a simplified schematic of

the logic affected by the COM2x[1:0] bit setting. The I/O Registers, I/O bits, and I/O pins in the figure are

shown in bold. Only the parts of the general I/O Port Control Registers (DDR and PORT) that are affected

by the COM2x[1:0] bits are shown. When referring to the OC2x state, the reference is for the internal

OC2x Register, not the OC2x pin.

Figure 19-4. Compare Match Output Unit, Schematic

PORT

DDR

D Q

OCnx

D Q

Waveform

Generator

COMnx[1]

COMnx[0]

DATA BUS

FOCnx

clk

I/O

The general I/O port function is overridden by the Output Compare (OC2x) from the Waveform Generator

if either of the COM2x1:0 bits are set. However, the OC2x pin direction (input or output) is still controlled

by the Data Direction Register (DDR) for the port pin. The Data Direction Register bit for the OC2x pin

(DDR_OC2x) must be set as output before the OC2x 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 OC2x state before the output is

enabled. Note that some COM2x[1:0] bit settings are reserved for certain modes of operation. See