BCM20706 Data Sheet
PCM Interface
Slot Mapping
The BCM20706 supports up to three simultaneous full-duplex SCO or eSCO channels through the PCM
interface. These three channels are time-multiplexed onto the single PCM interface by using a time-slotting
scheme where the 8 kHz or 16 kHz audio sample interval is divided into as many as 16 slots. The number of
slots is dependent on the selected interface rate (128 kHz, 512 kHz, or 1024 kHz). The corresponding number
of slots for these interface rate is 1, 2, 4, 8, and 16, respectively. Transmit and receive PCM data from an SCO
channel is always mapped to the same slot. The PCM data output driver tristates its output on unused slots to
allow other devices to share the same PCM interface signals. The data output driver tristates its output after the
falling edge of the PCM clock during the last bit of the slot.
Frame Synchronization
The BCM20706 supports both short- and long-frame synchronization in both master and slave modes. In short-
frame synchronization mode, the frame synchronization signal is an active-high pulse at the audio frame rate
that is a single-bit period in width and is synchronized to the rising edge of the bit clock. The PCM slave looks
for a high on the falling edge of the bit clock and expects the first bit of the first slot to start at the next rising edge
of the clock. In long-frame synchronization mode, the frame synchronization signal is again an active-high pulse
at the audio frame rate; however, the duration is three bit periods and the pulse starts coincident with the first
bit of the first slot.
Data Formatting
The BCM20706 may be configured to generate and accept several different data formats. For conventional
narrowband speech mode, the BCM20706 uses 13 of the 16 bits in each PCM frame. The location and order of
these 13 bits can be configured to support various data formats on the PCM interface. The remaining three bits
are ignored on the input and may be filled with 0s, 1s, a sign bit, or a programmed value on the output. The
default format is 13-bit 2’s complement data, left justified, and clocked MSB first.
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.
Broadcom®
Bluetooth SoC
May 19, 2016 • 20706-DS202-R
Page 18
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