CS8415A-IZ Просмотр технического описания (PDF) - Cirrus Logic
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CS8415A-IZ Datasheet PDF : 42 Pages
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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
register bit. Depending on the clocking options se-
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
15
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