ATmega64A datasheet(162/392 Pages) ATMEL

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8160C–AVR–07/09

ATmega64A

18. Output Compare Modulator (OCM1C2)

18.1

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 C of the 16-bit

Timer/Counter1 and the Output Compare Unit of the 8-bit Timer/Counter2. For more details

about these Timer/Counters see “16-bit Timer/Counter (Timer/Counter1 and Timer/Counter3)”

on page 111 and “8-bit Timer/Counter2 with PWM” on page 146. Note that this feature is not

available in ATmega103 compatibility mode.

Figure 18-1. Output Compare Modulator, Block Diagram

When the modulator is enabled, the two Output Compare channels are modulated together as

shown in the block diagram (Figure 18-1).

18.2

Description

The Output Compare unit 1C and Output Compare unit 2 shares the PB7 port pin for output. The

outputs of the Output Compare units (OC1C and OC2) overrides the normal PORTB7 Register

when one of them is enabled (i.e., when COMnx1:0 is not equal to zero). When both OC1C and

OC2 are enabled at the same time, the modulator is automatically enabled.

The functional equivalent schematic of the modulator is shown on Figure . The schematic

includes part of the Timer/Counter units and the Port B pin 7 output driver circuit.Output Com-

pare Modulator, Schematic.

OC1C

OC1C/

OC2/PB7

Timer/Counter1

Timer/Counter2

OC2

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