Datasheet

22. OCM - Output Compare Modulator

22.1 Overview

The Output Compare Modulator (OCM) allows generation of waveforms modulated with a carrier

frequency. The modulator uses the outputs from the Output Compare Unit B of the 16-bit Timer/Counter3

and the Output Compare Unit of the 16-bit Timer/Counter4. For more details about these Timer/Counters

see 16-bit Timer/Counter. When the modulator is enabled, the two output compare channels are

modulated together as shown in the block diagram (as the following figure).

Figure 22-1. Output Compare Modulator, Block Diagram

OC3B

OC3B /

OC4B / PD2

Timer/Counter 3

Timer/Counter 4

OC4B

Related Links

TC1, 3, 4 - 16-bit Timer/Counter1, 3, 4 with PWM

22.2 Description

The Output Compare unit 3B and Output Compare unit 4B shares the PD2 port pin for output. The

outputs of the Output Compare units (OC3B and OC4B) overrides the normal PORTD2 Register when

one of them is enabled (that is, when COMnx[1:0] is not equal to zero). When both OC3B and OC4B are

enabled at the same time, it will also enable this modulator.

The functional equivalent schematic of the modulator is shown in the figure below. The schematic

includes part of the Timer/Counter units and the port D pin 2 output driver circuit. When the modulator is

enabled the type of modulation (logical AND or OR) can be selected by setting the PORTD2 Register as

‘1’.

Note: The DDRD2 controls the direction of the port independent of the COMnx[1:0] bit setting.

ATmega328PB

OCM - Output Compare Modulator

Datasheet Complete

DS40001906C-page 246