Rainbow Electronics ATmega128L - Manual (Page 155)

155
ATmega128(L)
2467B–09/01
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 106 and “8-bit Timer/Counter2 with PWM” on page 140. Note
that this feature is not available in ATmega103 compatibility mode.
Figure 71. 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 71).
Description The output compare unit 1C and output compare unit 2 shares the PB7 port pin for out-
put. 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 auto-
matically enabled.
The functional equivalent schematic of the modulator is shown on Figure 72. The sche-
matic includes part of the Timer/Counter units and the port B pin 7 output driver circuit.
Figure 72. Output Compare Modulator, Schematic
OC1C
Pin
OC1C /
OC2 / PB7
Timer/Counter 1
Timer/Counter 2 OC2
PORTB7 DDRB7
D Q D Q
Pin
COM21
COM20
DATABUS
OC1C /
OC2 / PB7
COM1C1
COM1C0 Modulator
1
0
OC1C
D Q
OC2
D Q
( From Waveform Generator )
( From Waveform Generator )
0
1
Vcc