ATmega640/1280/1281/2560/2561
Output Compare
Modulator
(OCM1C0A)
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/Counter0, Timer/Counter1,
Timer/Counter3, Timer/Counter4, and Timer/Counter5 Prescalers” on page 169 and “8-
bit Timer/Counter2 with PWM and Asynchronous Operation” on page 173.
Figure 64. 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 64).
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 nor-
mal 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 65. The sche-
matic includes part of the Timer/Counter units and the port B pin 7 output driver circuit.
Figure 65. 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
171
2549A–AVR–03/05
ATMEL [ ATMEL ]
