DS580F6

13

CS8406

5. AES3 TRANSMITTER

The CS8406 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 “Appendix B: Channel Status and User

Data Buffer Management” on page 36.

The AES3 transmitter encodes and transmits audio anddigital 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 directly or through a transformer. The transmitter is

clocked from the clock input pin, OMCK. If OMCK is asynchronous to the data source, an interrupt bit (TSLIP) is

provided that will go high every time a data sample is dropped or repeated.

The channel status (C) and user (U) bits in the transmitted data stream are taken from storage areas within the

CS8406. The user can access the internal storage or configure the CS8406 to run in one of several automatic

modes. “Appendix B: Channel Status and User Data Buffer Management” on page 36 provides detailed descriptions

of each automatic mode and describes methods of accessing the storage areas. The transmitted user bit data can

optionally be input through the U pin, under the control of a control port register bit.

Figures 8 and 9 show the C/U/V timing requirements.

5.1

TXN and TXP Drivers

The AES3 transmitter line drivers are low skew, low impedance, differential outputs capable of driving ca-

bles directly. Both drivers are set to ground during reset (RST = LOW), when no AES3 transmit clock is pro-

vided, and optionally under the control of a register bit. The CS8406 also allows immediate muting of the

AES3 transmitter audio data through a control register bit.

External components are used to terminate and isolate the external cable from the CS8406. These compo-

nents are detailed in “Appendix A: External AES3/SPDIF/IEC60958 Transmitter Components” on page 35.

5.2

Mono Mode Operation

An alternate method for transmitting an AES3 192 kHz sample rate stream is Mono Mode. Mono Mode is

implemented by using the two sub-frames in a 96 kHz biphase encoded stream to carry consecutive sam-

ples of a single channel of a 192 kHz PCM stream (i.e. a mono signal). This allows older equipment, whose

AES3 transmitters and receivers are not rated for 192 kHz frame rate operation, to handle 192 kHz sample

rate information. In this Mono Mode, two AES3 cables and two CS8406's are needed for stereo data trans-

fer. The CS8406 is set to Mono Mode by the MMT control bit.

In Mono Mode, the input port will run at the audio sample rate (Fs), while the AES3 transmitter frame rate

will be at Fs/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 Mono Mode is only necessary if the incoming audio sample rate is already at 192 kHz and contains

both left and right audio data words. The “Mono Mode” AES3 output stream may also be achieved by keep-

ing the CS8406 in normal stereo mode, and placing consecutive audio samples in the left and right positions

in an incoming 96 kHz word rate data stream. Figure 9 shows the C/U/V timing requirements.

5.3

Transmitted Frame and Channel Status Boundary Timing

The TCBL pin is used to 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 contro l the precise timing of the transmitted AES3 frame

boundaries. This may be achieved in two ways: