ATmega64A datasheet(163/392 Pages) ATMEL

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163

8160C–AVR–07/09

ATmega64A

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

the PORTB7 Register. Note that the DDRB7 controls the direction of the port independent of the

COMnx1:0 bit setting.

18.2.1

Timing Example

Figure 18-2 illustrates the modulator in action. In this example the Timer/Counter1 is set to oper-

ate in fast PWM mode (non-inverted) and Timer/Counter2 uses CTC waveform mode with toggle

Compare Output mode (COMnx1:0 = 1).

Figure 18-2. Output Compare Modulator, Timing Diagram

In this example, Timer/Counter2 provides the carrier, while the modulating signal is generated

by the Output Compare unit C of the Timer/Counter1.The resolution of the PWM signal (OC1C)

is reduced by the modulation. The reduction factor is equal to the number of system clock cycles

of one period of the carrier (OC2). In this example the resolution is reduced by a factor of two.

The reason for the reduction is illustrated in Figure 18-2 at the second and third period of the

PB7 output when PORTB7 equals zero. The period 2 high time is one cycle longer than the

period three high time, but the result on the PB7 output is equal in both periods.

PORTB7

DDRB7

COM21

COM20

DATA BUS

OC1C /

OC2 / PB7

COM1C1

COM1C0

Modulator

OC1C

OC2

( From Waveform Generator )

Vcc

OC2

(CTC Mode)

OC1C

(FPWM Mode)

PB7

(PORTB7 = 0)

PB7

(PORTB7 = 1)

(Period)

clk

I/O

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