ATMEGA640 datasheet(167/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

19. Output Compare Modulator (OCM1C0A)

19.1 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/Counter0. For more details about these Timer/Counters see “Timer/Counter 0, 1, 3, 4, and 5

Prescaler” on page 164 and “8-bit Timer/Counter2 with PWM and Asynchronous Operation” on page 169.

Figure 19-1. Output Compare Modulator, Block Diagram

When the modulator is enabled, the two output compare channels are modulated together as shown in the block

diagram (see Figure 19-1).

19.2 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 OC0A) overrides the normal PORTB7 Register when one of them is enabled

(that is, when COMnx1:0 is not equal to zero). When both OC1C and OC0A are enabled at the same time, the

modulator is automatically enabled.

The functional equivalent schematic of the modulator is shown on Figure 19-2. The schematic includes part of the

Timer/Counter units and the port B pin 7 output driver circuit.

Figure 19-2. Output Compare Modulator, Schematic

When the modulator is enabled the type of modulation (logical AND or OR) can be selected by the PORTB7 Reg-

ister. Note that the DDRB7 controls the direction of the port independent of the COMnx1:0 bit setting.

OC1C

OC1C /

OC0A / PB7

Timer/Counter 1

Timer/Counter 0

OC0A

PORTB7

DDRB7

COMA01

COMA00

DATABUS

OC1C /

OC0A/ PB7

COM1C1

COM1C0

Modulator

OC1C

OC0A

( From Waveform Generator )

Vcc

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