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PCM Interface

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 46

Wideband Speech Support

When the host encodes Wideband Speech (WBS) packets in transparent mode, the encoded packets are

transferred over the PCM bus for an eSCO voice connection. In this 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. The BCM4354 also

supports slave transparent mode using a proprietary rate-matching scheme. In SBC-code mode, linear 16-bit

data at 16 kHz (256 Kbps rate) is transferred over the PCM bus.

Multiplexed Bluetooth and FM Over PCM

In this mode of operation, the BCM4354 multiplexes both FM and Bluetooth audio PCM channels over the same

interface, reducing the number of required I/Os. This mode of operation is initiated through an HCI command

from the host. The format of the data stream consists of three channels: a Bluetooth channel followed by two

FM channels (audio left and right). In this mode of operation, the bus data rate only supports 48 kHz operation

per channel with 16 bits sent for each channel. This is done to allow the low data rate Bluetooth data to coexist

in the same interface as the higher speed I2S data. To accomplish this, the Bluetooth data is repeated six times

for 8 kHz data and three times for 16 kHz data. An initial sync pulse on the PCM_SYNC line is used to indicate

the beginning of the frame.

To support multiple Bluetooth audio streams within the Bluetooth channel, both 16 kHz and 8 kHz streams can

be multiplexed. This mode of operation is only supported when the Bluetooth host is the master. Figure 9 shows

the operation of the multiplexed transport with three simultaneous SCO connections. To accommodate

additional SCO channels, the transport clock speed is increased. To change between modes of operation, the

transport must be halted and restarted in the new configuration.

Figure 9: Functional Multiplex Data Diagram

PCM_SYNC

PCM_IN

PCM_OUT

FM Right

FM Left

FM Right

FM Left

BT SCO 1 Tx

BT SCO 2 Tx

BT SCO 3 Tx

BT SCO 1 Rx

BT SCO 2 Rx

BT SCO 3 Rx

1 Frame

PCM_CLK

16 bits per SCO frame

CLK

16 bits per frame

Each SCO channel duplicates the data 6 times. Each WBS

frame duplicates the data three times per frame

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