CS8405A-CS datasheet(12/36 Pages) CIRRUS

12 / 36 page

CS8405A

DS469PP4

5. AES3 TRANSMITTER

The CS8405A includes an AES3 digital audio

transmitter. A comprehensive buffering scheme

provides write access to the channel status and user

data. This buffering scheme is described in “Ap-

pendix B: Channel Status and User Data Buffer

Management” on page 34.

The AES3 transmitter encodes and transmits audio

and digital data according to the AES3, IEC60958

(S/PDIF), and EIAJ CP-1201 interface standards.

Audio and control data are multiplexed together

and bi-phase mark encoded. The resulting bit

stream is driven to an output connector either di-

rectly or through a transformer. The transmitter is

clocked from the clock input pin, OMCK. If

OMCK is asynchronous to the data source, an in-

terrupt bit(TSLIP) is provided that will go high ev-

ery time a data sample is dropped or repeated. Be

aware that the pattern of slips does not have hyster-

esis and so the occurrence of the interrupt condition

is not deterministic.

The channel status (C) and user (U) bits in the

transmitted data stream are taken from storage ar-

eas within the CS8405A. The user can manually

access the internal storage or configure the

CS8405A to run in one of several automatic modes.

“Appendix B: Channel Status and User Data Buffer

Management” on page 34 provides detailed de-

scriptions of each automatic mode and describes

methods of manually accessing the storage areas.

The transmitted user bit data can optionally be in-

put through the U pin, under the control of a control

port register bit. Figure 7 shows the timing require-

ments for inputting U data through the U pin.

5.1

Transmitted Frame and Channel

Status Boundary Timing

The TCBL pin is used to control or indicate the

start of transmitted channel status block boundaries

and may be an input or an output.

In some applications, it may be necessary to control

the precise timing of the transmitted AES3 frame

boundaries. This may be achieved in two ways:

a) With TCBL set to input, driving TCBL high for

>3 OMCK clocks will cause a frame start, as well

as a new channel status block start.

b) If the serial audio input port is in slave mode and

TCBL is set to output, the start of the A channel

sub-frame will be aligned with the leading edge of

ILRCK.

5.2

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 CS8405A also allows immediate muting of the

AES3 transmitter audio data through a control reg-

ister bit.

External components are used to terminate and iso-

late the external cable from the CS8405A. These

components are detailed in “Appendix A: External

AES3/SPDIF/IEC60958

Transmitter

Compo-

nents” on page 33.

5.3

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 ca-

ble. 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 signal, re-

sulting in a 96 kHz sample rate stream. This allows

older equipment, whose AES3 transmitters and re-

ceivers are not rated for 96 kHz frame rate opera-

tion, to handle 96 kHz sample rate information. In

this “mono mode”, two AES3 cables are needed for

stereo data transfer. The CS8405A offers mono

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