Specifications

15
3.2 PCM Interface
The BCM-DC100-AS includes a PCM interface that shares pins with the I2S interface. The PCM
Interface on the BCM-DC100-AS can connect
to linear PCM codec devices in master or slave mode. In master mode, the BCM-DC100-AS generates
the PCM_CLK and PCM_SYNC
signals. In slave mode, these signals are provided by another master on the PCM interface and are
inputs to the BCM-DC100-AS.
3.2.1 Slot Mapping
The BCM-DC100-AS 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.
3.2.2 Frame Synchronization
The BCM-DC100-AS 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.