CS8415A-CS datasheet(15/42 Pages) CIRRUS

15 / 42 page

CS8415A

QCRC and CCRC errors do not affect the current

audio sample, even if unmasked.

5.5

Channel Status Data Handling

The first 2 bytes of the Channel Status block are

decoded into the Receiver Channel Status regis-

ter. The setting of the CHS bit in the Channel Sta-

tus Data Buffer Control register determines

whether the channel status decodes are from the A

channel (CHS = 0) or B channel (CHS = 1).

The PRO (professional) bit is extracted directly.

For consumer data, the COPY (copyright) bit is ex-

tracted, and the category code and L bits are de-

coded to determine SCMS status, indicated by the

ORIG (original) bit. If the category code is set to

General on the incoming AES3 stream, copyright

will always be indicated even when the stream in-

dicates no copyright. Finally, the AUDIO bit is ex-

tracted and used to set an AUDIO indicator, as

described in the Non-Audio Auto-Detection section

below.

If 50/15 µs pre-emphasis is detected, the state of

the EMPH pin is adjusted accordingly.

The encoded channel status bits which indicate

sample word length are decoded according to

AES3-1992 or IEC 60958. Audio data routed to the

serial audio output port is unaffected by the word

length settings; all 24 bits are passed on as re-

ceived.

Appendix A describes the overall handling of

Channel Status and User data.

5.6

User Data Handling

The incoming user data is buffered in a user acces-

sible buffer. Received User data may also be out-

put to the U pin under the control of a control

lected, there may not be a clock available to qualify

the U data output. Figure 7 illustrates the timing. If

the incoming user data bits have been encoded as

Q-channel subcode, the data is decoded and pre-

sented in 10 consecutive register locations. An in-

terrupt may be enabled to indicate the decoding of

a new Q-channel block, which may be read

through the control port.

5.7

Non-Audio Auto-Detection

An AES3 data stream may be used to convey non-

audio data, thus it is important to know whether the

incoming AES3 data stream is digital audio or not.

This information is typically conveyed in channel

status bit 1 (AUDIO), which is extracted automati-

cally by the CS8415A. However, certain non-audio

sources, such as AC-3 or MPEG encoders, may

not adhere to this convention, and the bit may not

be properly set. The CS8415A AES3 receiver can

detect such non-audio data. This is accomplished

by looking for a 96-bit sync code, consisting of

0x0000, 0x0000, 0x0000, 0x0000, 0xF872, and

0x4E1F. When the sync code is detected, an inter-

nal AUTODETECT signal will be asserted. If no ad-

ditional sync codes are detected within the next

4096 frames, AUTODETECT will be de-asserted

until another sync code is detected. The AUDIO bit

in the Receiver Channel Status register is the logi-

cal OR of AUTODETECT and the received chan-

nel status bit 1. If non-audio data is detected, the

data is still processed exactly as if it were normal

audio. It is up to the user to mute the outputs as re-

quired.

5.8

Mono Mode Operation

An AES3 stream may be used in more than one

way to transmit 96 kHz sample rate data. One

method is to double the frame rate of the current

format. This results in a stereo signal with a sample

rate of 96 kHz, carried over a single twisted pair

cable. An alternate method is implemented using

the 2 sub-frames in a 48 kHz frame rate AES3 sig-

nal to carry consecutive samples of a mono signal,

resulting in a 96 kHz sample rate stream. This al-

lows older equipment, whose AES3 transmitters

and receivers are not rated for 96 kHz frame rate

operation, to handle 96 kHz sample rate informa-

tion. In this “mono mode”, 2 AES3 cables are need-

ed for stereo data transfer. The CS8415A offers

mono mode operation, controlled through the

MMR control register bit.

The receiver mono mode effectively doubles Fs

compared to the input frame rate. The clock output

on the RMCK pin tracks Fs, and so is doubled in

frequency compared to stereo mode. The receiver

will run at a frame rate of Fs/2, and the serial audio

output port will run at Fs. Sub-frame A data will be

CS8415A-CS датащи(PDF) 15 Page - Cirrus Logic

CS8415A-CS датащи(HTML) 15 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

датащи скачать

ссылки URL