ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 160

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

Timing Example
160
ATmega64(L)
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.
Figure 74 illustrates the modulator in action. In this example the Timer/Counter1 is set to
operate in fast PWM mode (non-inverted) and Timer/Counter2 uses CTC waveform
mode with toggle Compare Output mode (COMnx1:0 = 1).
Figure 74. Output Compare Modulator, Timing Diagram
In this example, Timer/Counter2 provides the carrier, while the modulating signal is gen-
erated 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 74 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.
(FPWM Mode)
(PORTB7 = 0)
(PORTB7 = 1)
(CTC Mode)
(Period)
OC1C
clk
OC2
PB7
PB7
I/O
1
2
3
2490G–AVR–03/04