Datasheet

166
7593L–AVR–09/12
AT90USB64/128
17. Output Compare Modulator (OCM1C0A)
17.1 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/Counter0, Timer/Counter1, and Timer/Counter3 pres-
calers” on page 96 and “8-bit Timer/Counter2 with PWM and asynchronous operation” on page
145.
Figure 17-1. Output Compare Modulator, block diagram.
When the modulator is enabled, the two output compare channels are modulated together as
shown in the block diagram (Figure 17-1).
17.2 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 17-2. The schematic
includes part of the Timer/Counter units and the port B pin 7 output driver circuit.
Figure 17-2. 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