Cirrus-logic AN22 Manual do Utilizador descarregar pdf (Página 1)

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Cirrus Logic, Inc. 1998

Cirrus Logic, Inc.

Crystal Semiconductor Products Division

P.O. Box 17847, Austin, Texas 78760

(512) 445 7222 FAX: (512) 445 7581

http://www.crystal.com

AN22

Application Note

OVERVIEW OF DIGITAL AUDIO INTERFACE

DATA STRUCTURES

Clif Sanchez & Roger Taylor

The following information is provided for conve-

nience, but by no means constitutes the entire spec-

ification. Also included is information from the

IEC958 and the new AES3-199x and TC84 docu-

ments. The AES3-199x and TC84 documents have

not received approval as of the printing of this data

sheet. To guarantee conformance, a copy of the ac-

tual specification should be obtained from the Au-

dio Engineering Society or ANSI (ANSI

S4.40-1985) for the AES3 document, and the Inter-

national Electrotechnical Commission for the

IEC958 document.

The AES/EBU interface is a means for serially

communicating digital audio data through a single

transmission line. It provides two channels for au-

dio data, a method for communicating control in-

formation, and some error detection capabilities.

The control information is transmitted as one bit

per sample and accumulates in a block structure.

The data is biphase encoded, which enables the re-

ceiver to extract a clock from the data. Coding vio-

lations, defined as preambles, are used to identify

sample and block boundaries.

Frames Sub-frames and Blocks

An audio sample is placed in a structure known as

a sub-frame. The sub-frame, shown in Figure 1,

consists of 4 bits of preamble, 4 bits of auxiliary

data, 20 bits of audio data, 3 bits called validity, us-

er, and channel status, and a parity bit. The pream-

ble contains biphase coding violations and

identifies the start of a sub-frame. The audio sam-

ple word length can vary up to 24 bits and is trans-

mitted LSB first. If the word length is greater than

20 bits, the sample occupies both the audio and

FEB ‘98

AN22REV2

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Resumo do Conteúdo

Página 1 - Application Note

Página 2 - Modulation and Preambles

Página 3 - AN22REV2 3

AN222 AN22REV2auxiliary data fields. If it is 20 bits or less, the aux-iliary field can be used for other applications suchas voice. The parity bit ge

Página 4 - 4 AN22REV2

AN22AN22REV2 3for each channel and one to indicate the beginningof a channel status block (which is also channelA).To distinguish the preambles from a

Página 5 -

AN224 AN22REV2Table 1 lists the preamble biphase-mark data pat-terns and what each designates. Since bi-phase-mark encoding is not polarity conscious,

Página 6 - 6 AN22REV2

AN22AN22REV2 5 BYTE 2bits 0 1 2 AUX: Use of auxiliary sample bits0 0 0 Not defined. Maximum audio word lengthis 20 bits0 0 1 Used for main audio.

Página 7 - AN22REV2 7

AN226 AN22REV2Channel Status Block - Consumer FormatSetting the first bit of channel status low designatesthe consumer format. The channel status bloc

Página 8 - 8 AN22REV2

AN22AN22REV2 7Currently the standards committees are trying todefine a minimum implementation as well as levelsof implementation of channel status dat

Página 9 - • Notes •

AN228 AN22REV2source has copy protection asserted, then the L bitmust be used to determine whether the data can berecorded.The L bit determines whethe

Página 10

• Notes •

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