Cirrus Logic CS8427 - Manual (Page 19)

CS8427
DS477F5 19
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 two sub-frames in a 48-kHz frame rate AES3
signal to carry consecutive samples of a mono sig-
nal, resulting in a 96-kHz sample rate stream. This
allows 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”, two AES3 cables are
needed for stereo data transfer. The CS8427 of-
fers mono mode operation for the AES3 receiver
and the AES3 transmitter. The receiver and trans-
mitter sections may be independently set to mono
mode through the MMR and MMT control bits.
8.1 Receiver Mono Mode
The receiver mono mode effectively doubles the
input frame rate, Fsi. The clock output on the
RMCK pin tracks Fsi, and thus is doubled in fre-
quency compared to stereo mode. The receiver
will run at a frame rate of Fsi/2, and the serial audio
output port will run at Fsi. Sub-frame A data will be
routed to both the left and right data fields on
SD-OUT. Similarly, sub-frame B data will be routed
to both the left and right data fields of the next word
clock cycle of SDOUT.
Using receiver mono mode is only necessary if the
serial audio output port must run at 96 kHz. If the
CS8427 is kept in normal stereo mode and re-
ceives AES3 data arranged in mono mode, the se-
rial audio output port will run at 48 kHz, with left
and right data fields representing consecutive au-
dio samples.
8.2 Transmitter Mono Mode
In transmitter mono mode, the input port will run at
the audio sample rate (Fso), while the AES3 trans-
mitter frame rate will be at Fso/2. Consecutive left
or right channel serial audio data samples may be
selected for transmission on the A and B sub-
frames, and the channel status block transmitted is
also selectable.
Using transmitter mono mode is only necessary if
the incoming audio sample rate is already at
96 kHz and contains both left and right audio data
words. The “mono mode” AES3 output stream may
also be achieved by keeping the CS8427 in normal
stereo mode and placing consecutive audio sam-
ples in the left and right positions of an incoming
data stream with a 48-kHz word rate.
Serial
Audio
Input
AES3
Encoder
Serial
Audio
Output
Receiver
RXP
RXN
ILRCK
ISCLK
SDIN
OLRCK
OSCLK
SDOUT
TXP
TXN
AES3
TXOFF AESBP
SPD
TXD
MUX
MUX
Figure 7. Software Mode Audio Data Flow Switching Options