Txn And Txp Drivers; Mono Mode Operation; Receiver Mono Mode; Transmitter Mono Mode - Cirrus Logic Crystal CS8427 Series Preliminary Product Information

4.3.2

TXN and TXP Drivers

The line drivers are low skew, low impedance, dif-
ferential outputs capable of driving cables directly.
Both drivers are set to ground during reset (RST =
low), when no AES3 transmit clock is provided,
and optionally under the control of a register bit.
The CS8427 also allows immediate mute of the
AES3 transmitter audio data via a control register
bit.
External components are used to terminate and iso-
late the external cable from the CS8427. These
components are detailed in the Appendix "External
AES/SPDIF/IEC60958 Transmitter and Receiver
Components".

4.4 Mono Mode Operation

The AES3 standard is currently being updated to
include options for 96kHz sample rate operation.
One method is to double the frame rate of the cur-
rent 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 us-
ing the two sub-frames in a 48kHz frame rate AES3
signal to carry consecutive samples of a mono sig-
nal, resulting in a 96kHz sample rate stream. This
allows older equipment, whose AES3 transmitters
and receivers are not rated for 96kHz frame rate op-
eration, to handle 96kHz sample rate information.
In this "mono mode", two AES3 cables are needed
for stereo data transfer. The CS8427 offers mono
mode operation for the AES3 receiver and the
AES3 transmitter. The receiver and transmitter sec-
tions may be independently set to mono mode via
the MMR and MMT control bits.
DS477PP1
4.4.1

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 out-
put 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 96kHz. If the
CS8427 is kept in normal stereo mode and re-
ceives AES3 data arranged in mono mode, the seri-
al audio output port will run at 48kHz, with left and
right data fields representing consecutive audio
samples.
4.4.2

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 via 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 96kHz
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 ste-
reo mode and placing consecutive audio samples in
the left and right positions of an incoming data
stream with a 48kHz word rate.
CS8427
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