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PCM Interface

BCM20705 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

Bluetooth Transceiver and Baseband Processor

November 13, 2014 • MCS20705-DS104-R

Page 29

Slot Mapping

The device supports up to three simultaneous, full-duplex SCO or eSCO channels. These channels are time-

multiplexed onto the PCM interface using a time slotting scheme based on the audio sampling rate, as described

in Table 3.

Transmit and receive PCM data from an SCO channel is always mapped to the same slot. The PCM data output

driver tri-states its output on unused slots to allow other devices to share the same PCM interface signals. The

data output driver tri-states its output after the falling edge of the PCM clock during the last bit of the slot.

Wideband Speech

The BCM20705 provides support for Wideband Speech (WBS) in two ways:

• Transparent mode

The host encodes WBS packets and the encoded packets are

transferred over the PCM bus for SCO or eSCO voice connections.

In Transparent mode, the PCM bus is typically configured in master

mode for a 4 kHz sync rate with 16-bit samples, resulting in a

64 kbps bit rate.

• On-chip SmartAudio® technology

The BCM20705 can perform Subband-Codec (SBC) encoding and

decoding of linear 16 bits at 16 kHz (256 kbps rate) transferred over

the PCM bus.

Table 3: PCM Interface Time Slotting Scheme

Audio Sample Rate Time Slotting Scheme

8 kHz

The number of slots depends on the selected interface rate, as follows:

Interface rate

Slot

128

256

512

1024

2048

16 kHz

The number of slots depends on the selected interface rate, as follows:

Interface rate

Slot

256

512

1024

2048

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