ADSP-214xx SHARC Processor Hardware Reference C-11
Audio Frame Formats
2. Preamble X indicates the start of a channel A subframe when not at
the start of a block.
3. Preamble Y indicates the start of a channel B subframe.
The user bits from the channel A and B subframes are simply strung
together. For more information, please refer to the AES3 standard.
The data carried by the SPDIF interface is transmitted serially. In order to
identify the assorted bits of information the data stream is divided into
frames, each of which are 64 time slots (or 128 unit intervals
1
) in length
(Figure C-4). Since the time slots correspond with the data bits, the frame
is often described as being 64 bits in length.
A frame is uniquely composed of two subframes. The first subframe nor-
mally starts with preamble X. However, the preamble changes to preamble
Z once every 192 frames. This defines the block of frames structure used
to organize the channel status information. The second subframe always
starts with preamble Y.
Figure C-4. S/PDIF Block Structure
1
The unit interval is the minimum time interval between condition changes of a data transmission sig-
nal.
CHANNEL
1
X Y
CHANNEL
2
ZY
CHANNEL
1
CHANNEL
2
CHANNEL
1
CHANNEL
2
X
Y
START OF
BLOCK
SUBFRAME
1
SUBFRAME
2
FRAME 0
FRAME 191 FRAME 1
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