11-8
Audio Decoder Module
The 16-, 20-, or 24-bit decoded audio samples that are input to the DAC
interface are converted to 32-bit serial output (ASDATA). This format is
obtained by sign extension of the input data.
The S/P DIF (IEC958) interface supports 16-bit data samples from the
audio decoders and formatters (optional 20- and 24-bit stream widths for
LPCM (L64021D)). The formatters preserve the Musicam multichannel
extentions for true multichannel S/P DIF output (up to 7.1 channels). The
formatters also reformat multichannel Dolby Digital audio streams (up to
5.1 channels) and DTS audio streams (up to 8 channels) for S/P DIF
output. The S/P DIF interface produces a xed-length, 32-bit packet per
input sample and then represents each bit with two consecutive binary
states (biphase mark) as a clock self-recovery technique.
In the PCM FIFO mode, the host writes decoded PCM audio bytes into
a FIFO through a register in the Host Interface. According to the mode
selected, the outputs of the appropriate decoder and formatter and the
PCM FIFO are steered through the two multiplexers to the DAC and
S/P DIF interfaces.
One of the ACLK inputs is selected by the host and divided into three
clocks according to host divider selection. The two derived BCLKs
convert the parallel inputs to the interfaces to serial outputs. The DAC
BCLK is supplied to the external DAC as a bit clock. The divider also
supplies the DAC clock (A_ACLK) to the output multiplexer. The host
must select the proper divider to match the DAC.
The two output multiplexers can bypass the Audio Decoder entirely and
turn the S/P DIF and CD inputs around to the output pins. This feature
lets the L64021 Decoder share a DAC in the system with a CD decoder.
11.3 Decoding Flow Control
The rst part of this section gives brief descriptions of the following
register bits and elds; Audio Decoder Play Mode, Audio Decoder
Start/Stop, Audio Formatter Play Mode, and Audio Formatter Start/Stop
.
The second part describes the procedures you should follow to start and
stop the Audio Decoder properly.