User's Manual

Silicon Laboratories Finland Oy
Page 34 of 51
9 PCM Codec Interface
PCM is a standard method used to digitize audio (particularly voice) for transmission over digital communication
channels. Through its PCM interface, WT11u has hardware support for continual transmission and reception of
PCM data, thus reducing processor overhead for wireless headset applications. WT11u offers a bidirectional
digital audio interface that routes directly into the baseband layer of the on-chip firmware. It does not pass
through the HCI protocol layer.
Hardware on WT11u allows the data to be sent to and received from a SCO connection. Up to three SCO
connections can be supported by the PCM interface at any one time.
WT11u can operate as the PCM interface master generating an output clock of 128, 256 or 512kHz. When
configured as PCM interface slave, it can operate with an input clock up to 2048kHz. WT11u is compatible with
a variety of clock formats, including Long Frame Sync, Short Frame Sync and GCI timing environments.
It supports 13-bit or 16-bit linear, 8-bit µ-law or A-law companded sample formats at 8ksamples/s and can
receive and transmit on any selection of three of the first four slots following PCM_SYNC. The PCM
configuration options are enabled by setting PSKEY_PCM_CONFIG32.
WT11u interfaces directly to PCM audio devices.
NOTE: Analog audio lines are very sensitive to RF disturbance. Use good layout practices to ensure noise less
audio. Make sure that the return path for the audio signals follows the forward current all the way as close as
possible and use fully differential signals when possible. Do not compromise audio routing.
9.1 PCM Interface Master/Slave
When configured as the master of the PCM interface, WT11u generates PCM_CLK and PCM_SYNC.
Figure 26: PCM Interface Master
When configured as the Slave of the PCM interface, WT11u accepts PCM_CLK rates up to 2048kHz.