CS8427-CSZ datasheet(17/59 Pages) CIRRUS

17 / 59 page

CS8427

DS477F3

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 B: Channel Status and User Data Buffer

Management” on page 51 describes the overall

handling of Channel Status and User bit data.

6.5

User Data Handling

The incoming user data is buffered in a user acces-

sible buffer. Various automatic modes of re-trans-

mitting received User data are provided. The

Appendix: Channel Status and User Data Buffer

Management describes the overall handling of CS

and U data.

Received User data may also be output to the U

pin, under the control of a control register bit. De-

pending on the data flow and clocking options se-

lected, there may not be a clock available to qualify

the U data output. Figure 13 illustrates the timing.

If the incoming user data bits have been encoded

as Q-channel subcode, the data is decoded and

presented in ten consecutive register locations. An

interrupt may be enabled to indicate the decoding

of a new Q-channel block, which may be read

through the control port.

6.6

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 CS8427. However, certain non-audio

sources, such as AC3® or MPEG encoders, may

not adhere to this convention, and the bit may not

be properly set. The CS8427 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.

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