Datasheet

2003 Apr 10 31
NXP Semiconductors Preliminary specification
Stereo audio codec with SPDIF interface UDA1355H
9 SPDIF SIGNAL FORMAT
9.1 SPDIF channel encoding
The digital signal is coded using Biphase Mark Code
(BMC), which is a kind of phase modulation. In this
scheme, a logic 1 in the data corresponds to two
zero-crossings in the coded signal, and a logic 0 to one
zero-crossing. An example of the encoding is given in
Fig.11.
9.2 SPDIF hierarchical layers
The SPDIF signal format is shown in Fig.12. A PCM signal
is transmitted in sequential blocks. Each block consists
of 192 frames. Each frame contains two sub-frames, one
for each channel. Each subframe is preceded by a
preamble. There are three types of preambles: B, M
and W. Preambles can be spotted easily in an SPDIF
bitstream because these sequences never occur in the
channel parts of a valid SPDIF bitstream.
The sub-frame format is represented by Fig.13.
A sub-frame contains a single audio sample word which
may be 24 bits wide, a validity bit which indicates whether
the sample is valid, a bit containing user data, a bit
indicating the channel status and a parity bit for this
sub-frame.
The data bits 31 to 4 in each sub-frame are encoded using
a BMC scheme. The sync preamble contains a violation of
the BMC scheme and can be detected. Table 15 indicates
the values of the preambles.
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data
clock
BMC
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Fig.11 Biphase mark encoding.
Fig.12 SPDIF signal format
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channel 1MMMWW WBchannel 2 channel 1
sub-frame
channel 2 channel 1 channel 2 channel 1 channel 2
frame 0 frame 191frame 191
block
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sub-frame
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sync
preamble
auxiliary
03478 27 28 31
L
S
B
L
S
B
M
S
B
Paudio sample word
CUV
validity flag
user data
channel status
parity bit
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Fig.13 Sub-frame format