www.ti.com

OVERSAMPLING RATE CONTROL

ZERO FLAGS (PCM1780/82)

Zero-Detect Condition

Zero-Flag Outputs

ZERO FLAG (PCM1781)

HARDWARE CONTROL (PCM1781)

PCM1780, PCM1781, PCM1782

SLES132A – MARCH 2005 – REVISED APRIL 2005

The PCM1780/81/82 automatically controls the oversampling rate of the delta-sigma D/A converters with the

Zero detection for each output channel is independent from the other. If the data for a given channel remains at a

0 level for 1024 sample periods (or LRCK clock periods), a zero-detect condition exists for that channel.

Each channel has a corresponding zero-flag pin, ZEROL (pin 1) or ZEROR (pin 16). Given that a zero-detect

condition exists for one or more channels, the zero-flag pins for those channels are set to a logic-1 state. The

zero-flag pins can be used to operate external mute circuits, or used as status indicators for a microcontroller,

audio signal processor, or other digitally controlled function.

The active polarity of the zero-flag outputs can be inverted by setting the ZREV bit of control register 22 to 1. The

reset default is active-high output, or ZREV = 0.

The L-channel and R-channel common zero flag can be selected by setting the AZRO bit of control register 22

to 1. The reset default is for independent L-channel and R-channel zero flags, or AZRO = 0.

On the PCM1782, ZEROL and ZEROR are open-drain outputs.

The PCM1781 has a zero-flag pin, ZEROA (pin 16). ZEROA is the L-channel and R-channel common zero-flag

pin. If the data for L-channel and R-channel remains at a 0 level for 1024 sampling periods (or LRCK clock

periods), ZEROA is set to a logic-1 state.

The digital functions of the PCM1781 are capable of hardware control. Table 2 shows selectable formats, Table 3

shows de-emphasis control, and Table 4 shows muting control.

Table 2. Data Format Selection

FMT (PIN 1)

DATA FORMAT

LOW

HIGH

16-bit right-justified

Table 3. De-Emphasis Control

DEMP1 (PIN 3)

DEMP0 (PIN 2)

DE-EMPHASIS FUNCTION

LOW

LOW

OFF

LOW

HIGH

48-kHz de-emphasis ON

HIGH

LOW

44.1-kHz de-emphasis ON

HIGH

HIGH

32-kHz de-emphasis ON

Table 4. Mute Control

MUTE (PIN 4)

MUTE STATUS

LOW

Mute OFF

HIGH

Mute ON

16