Datasheet

172
2549O–AVR–05/12
ATmega640/1280/1281/2560/2561
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 169 and “8-
bit Timer/Counter2 with PWM and Asynchronous Operation” on page 174.
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
OC1C
Pin
OC1C /
OC0A / PB7
Timer/Counter 1
Timer/Counter 0
OC0A
PORTB7 DDRB7
DQDQ
Pin
COMA01
COMA00
DATABUS
OC1C /
OC0A/ PB7
COM1C1
COM1C0
Modulator
1
0
OC1C
DQ
OC0A
DQ
( From Waveform Generator )
( From Waveform Generator )
0
1
Vcc