Cirrus Logic CS8427 - Manual (Page 17)

CS8427
DS477F5 17
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 52
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.