Datasheet

ADAV801
Rev. A | Page 24 of 60
Serial Digital Audio Transmission Standards
The ADAV801 can receive and transmit S/PDIF, AES/EBU, and
IEC-958 serial streams. S/PDIF is a consumer audio standard,
and AES/EBU is a professional audio standard. IEC-958 has
both consumer and professional definitions. This data sheet is
not intended to fully define or to provide a tutorial for these
standards. Contact the international standards-setting bodies
for the full specifications.
All these digital audio communication schemes encode audio
data and audio control information using the biphase-mark
method. This encoding method minimizes the dc content of the
transmitted signal. As can be seen from
Figure 43, 1s in the
original data end up with midcell transitions in the biphase-
mark encoded data, while 0s in the original data do not. Note
that the biphase-mark encoded data always has a transition
between bit boundaries.
011100
04577-023
CLOCK
(
2 TIMES BIT
R
ATE)
BIPHASE-MARK
DATA
DATA
Figure 43. Biphase-Mark Encoding
Digital audio-communication schemes use preambles to
distinguish among channels (called subframes) and among
longer-term control information blocks (called frames). Pream-
bles are particular biphase-mark patterns, which contain encoding
violations that allow the receiver to uniquely recognize them.
These patterns and their relationship to frames and subframes
are shown in
Table 8 and Figure 44.
Table 8. Biphase-Mark Encode Preamble
Biphase Patterns Channel
X 11100010 or 00011101 Left
Y 11100100 or 00011011 Right
Z 11101000 or 00010111 Left and CS block start
XY ZY XY
04577-024
PREAMBLES
LEFT CH
FRAME 191 FRAME 0 FRAME 1
RIGHT CH LEFT CH RIGHT CH LEFT CH RIGHT CH
SUBFRAME SUBFRAME
Figure 44. Preambles, Frames, and Subframes
The biphase-mark encoding violations are shown in Figure 45.
Note that all three preambles include encoding violations.
Ordinarily, the biphase-mark encoding method results in a
polarity transition between bit boundaries.
11100010
11100100
11101000
04577-025
PREAMBLE X
PREAMBLE Y
PREAMBLE Z
Figure 45. Preambles
The serial digital audio communication scheme is organized
using a frame and subframe construction. There are two
subframes per frame (ordinarily the left and right channel).
Each subframe includes the appropriate 4-bit preamble, up to
24 bits of audio data, a validity (V) bit, a user (U) bit, a channel
status (C) bit, and an even parity (P) bit. The channel status bits
and the user bits accumulate over many frames to convey
control information. The channel status bits accumulate over a
192 frame period (called a channel status block). The user bits
accumulate over 1176 frames when the interconnect is imple-
menting the so-called subcode scheme (EIAJ CP-2401). The
organization of the channel status block, frames, and subframes
is shown in
Table 9 and Tabl e 10. Note that the ADAV801
supports the professional audio standard from a software
point of view only. The digital interface supports only
consumer mode.
Table 9. Consumer Audio Standard
Data Bits
Address
1
7 6 5 4 3 2 1 0
N
Channel
Status
Emphasis
Copy-
right
Non-
Audio
Pro/
Con
= 0
N + 1 Category Code
N + 2 Channel Number Source Number
N + 3 Reserved
Clock
Accuracy
Sampling Frequency
N + 4 Reserved Word Length
N + 5 to
(N + 23)
Reserved
1
N = 0x20 for receiver channel status buffer.
N = 0x38 for transmitter channel status buffer.