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CS8427-IS

96 kHz Digital Audio Interface Transceiver

Cirrus Logic 

CS8427

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.

ILRCK

ISCLK

SDIN

Serial

Audio

Input

RXN

RXP

AES3

Receiver

SPD

MUX

MUX

TXD

Serial

Audio

Output

AESBP TXOFF

AES3

Encoder

OLRCK

OSCLK

SDOUT

TXP

TXN

Figure 7. Software Mode Audio Data Flow Switching Options

DS477F1

19

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