Atmel ATmega128 User Manual

161
2467S–AVR–07/09
ATmega128
Output
Compare
Modulator
(OCM1C2)
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/Counter2. For more details
about these Timer/Counters see “16-bit Timer/Counter (Timer/Counter1 and Timer/Counter3)”
on page 112 and “8-bit Timer/Counter2 with PWM” on page 146. Note that this feature is not
available in ATmega103 compatibility mode.
Figure 72. Output Compare Modulator, Block Diagram
When the modulator is enabled, the two output compare channels are modulated together as
shown in the block diagram (Figure 72).
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 OC2) 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
OC2 are enabled at the same time, the modulator is automatically enabled.
The functional equivalent schematic of the modulator is shown on Figure 73. The schematic
includes part of the Timer/Counter units and the port B pin 7 output driver circuit.
Figure 73. Output Compare Modulator, Schematic
OC1C
Pin
OC1C /
OC2 / PB7
Timer/Counter 1
Timer/Counter 2
OC2
PORTB7 DDRB7
DQDQ
Pin
COM21
COM20
DATABUS
OC1C /
OC2 / PB7
COM1C1
COM1C0
Modulator
1
0
OC1C
DQ
OC2
DQ
( From Waveform Generator )
( From Waveform Generator )
0
1
Vcc

Atmel ATmega128 Specifications

General

Brand	Atmel
Model	ATmega128
Category	Microcontrollers
Language	English