ADAV801ASTZ datasheet(25/61 Pages) AD

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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.

CLOCK

(2 TIMES BIT RATE)

BIPHASE-MARK

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

11100010 or 00011101

Left

11100100 or 00011011

Right

11101000 or 00010111

Left and CS block start

PREAMBLES

LEFT CH

FRAME 191

FRAME 0

FRAME 1

RIGHT CH

LEFT CH

RIGHT CH

LEFT CH

RIGHT CH

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.

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 Table 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

Address1

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.

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