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PCM Interface

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 45

PCM Interface

The BCM4354 supports two independent PCM interfaces that share the pins with the I2S interfaces. The PCM

Interface on the BCM4354 can connect to linear PCM Codec devices in master or slave mode. In master mode,

the BCM4354 generates the PCM_CLK and PCM_SYNC signals, and in slave mode, these signals are provided

by another master on the PCM interface and are inputs to the BCM4354.

The configuration of the PCM interface may be adjusted by the host through the use of vendor-specific HCI

commands.

Slot Mapping

The BCM4354 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 of 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 BCM4354 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 BCM4354 may be configured to generate and accept several different data formats. For conventional

narrowband speech mode, the BCM4354 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.

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