Datasheet

177
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
16. Output Compare Modulator (OCM1C0A)
16.1 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 Prescalers” on page 92.
Figure 16-1. 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 16-1).
16.2 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 16-2. The schematic includes part of
the Timer/Counter units and the port B pin 7 output driver circuit.
Figure 16-2. Output Compare Modulator, Schematic
When the modulator is enabled the type of modulation (logical AND or OR) can be selected by the PORTB7
Register. When PORTB7=0, logical AND will be performed and when PORTB7=1, logical OR will be performed
(see Figure 16-3 on page 178).
Note that the DDRB7 controls the direction of the port independent of the COMnx1:0 bit setting.
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