Rainbow-electronics ATmega128L Uživatelský manuál stáhnout pdf (Strana 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

OC1C /

OC2 / PB7

Timer/Counter 1

Timer/Counter 2

OC2

PORTB7 DDRB7

DQDQ

COM21

COM20

DATABUS

OC1C /

OC2 / PB7

COM1C1

COM1C0

Modulator

OC1C

OC2

( From Waveform Generator )

Vcc

1 2 ... 150 151 152 153 154 155 156 157 158 159 160 ... 330 331

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