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 170 and “8-
bit Timer/Counter2 with PWM and Asynchronous Operation” on page 175.
Figure 19-1. Output Compare Modulator, Block Diagram
OC1C
Timer/Counter 1
Pin
OC1C /
OC0A / PB7
OC0A
Timer/Counter 0
When the modulator is enabled, the two output compare channels are modulated together as
shown in the block diagram (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 (i.e., 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
COMA01
COMA00
Vcc
COM1C1
COM1C0
Modulator
0
1
( From Waveform Generator )
D
Q
1
0
OC1C
Pin
OC1C /
( From Waveform Generator )
D
Q
OC0A/ PB7
OC0A
D
Q
D
Q
PORTB7
DDRB7
DATABUS
173
2549L–AVR–08/07
ATMEL [ ATMEL ]
