CYW20704
5.1.5 Multiplexed Bluetooth Over PCM
Bluetooth supports multiple audio streams within the Bluetooth channel and 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 5 shows the operation of the multiplexed trans-
port 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 5. Functional Multiplex Data Diagram
1 frame
BT SCO 1 Rx
BT SCO 1 Tx
BT SCO 2 Rx
BT SCO 2 Tx
BT SCO 3 Rx
BT SCO 3 Tx
PCM_OUT
PCM_IN
PCM_SYNC
PCM_CLK
CLK
16 bits per SCO frame
Each SCO channel duplicates the data 6 times. Each
WBS frame duplicates the data 3 times per frame
5.1.6 Burst PCM Mode
In this mode of operation, the PCM bus runs at a significantly higher rate of operation to allow the host to duty cycle its operation and
save current. In this mode of operation, the PCM bus can operate at a rate of up to 24 MHz. This mode of operation is initiated with
an HCI command from the host.
5.2 HCI Transport Detection Configuration
The CYW20704 supports the following interface types for the HCI transport from the host:
■ UART (H4)
■ USB
Only one host interface can be active at a time. The firmware performs a transport detect function at boot-time to determine which
host is the active transport. It can auto-detect UART and USB interfaces, but the SPI interface must be selected by strapping the
SCL pin to 0.
The complete algorithm is summarized as follows:
1. Determine if any local NVRAM contains a valid configuration file. If it does and a transport configuration entry is present, select
the active transport according to entry, and then exit the transport detection routine.
2. Look for start-of-frame (SOF) on the USB interface. If it is present, select USB.
3. Look for CTS_N = 0 on the UART interface. If it is present, select UART.
4. Repeat Step 2 and Step 3 until transport is determined.
Document Number: 002-14786 Rev. *E
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