CS8427-CSZ datasheet(16/60 Pages) CIRRUS

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CS8427

DS477F5

6. AES3 RECEIVER

The CS8427 includes an AES3 digital audio re-

ceiver and an AES3 digital audio transmitter. A

comprehensive

buffering

scheme

provides

read/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”.

The AES3 receiver accepts and decodes audio

and digital data according to the AES3, IEC60958

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

The receiver consists of a differential input stage,

accessed through pins RXP and RXN, a PLL

based clock recovery circuit, and a decoder which

separates the audio data from the channel status

and user data.

External components are used to terminate and

isolate the incoming data cables from the CS8427.

These components are detailed in “Appendix A:

External AES3/SPDIF/IEC60958 Transmitter and

Receiver Components” on page 50.

6.1

OMCK System Clock Mode

A special mode is available that allows the clock

that is being input through the OMCK pin to be out-

put through the RMCK pin. This feature is con-

trolled by the SWCLK bit in control register 1.

When the PLL loses lock, the frequency of the

VCO drops to 300 kHz. The SWCLK function al-

lows the clock from RMCK to be used as a clock in

the system without any disruption when input is re-

moved from the Receiver. This clock switching is

performed glitch free. None of the internal circuitry

that is clocked from the PLL is driven by the OMCK

being output from RMCK. This function is available

only in software mode.

6.2

PLL, Jitter Attenuation, and

Varispeed

Please see Appendix C for general description of

the PLL, selection of recommended PLL filter com-

ponents, and layout considerations. Figure 5

shows the recommended configuration of the two

capacitors and one resistor that comprise the PLL

filter.

6.3

Error Reporting and Hold Function

While decoding the incoming AES3 data stream,

the CS8427 can identify several kinds of error, in-

dicated in the Receiver Error register. The UN-

LOCK bit indicates whether the PLL is locked to

the incoming AES3 data. The V bit reflects the cur-

rent validity bit status. The BIP (bi-phase) error bit

indicates an error in incoming bi-phase coding.

The PAR (parity) bit indicates a received parity er-

ror.

The error bits are “sticky”: they are set on the first

occurrence of the associated error and will remain

set until the user reads the register through the

control port. This enables the register to log all un-

masked errors that occurred since the last time the

The Receiver Error Mask register allows masking

of individual errors. The bits in this register serve

as masks for the corresponding bits of the Receiv-

er Error Register. If a mask bit is set to 1, the error

is unmasked, which implies the following: its occur-

rence will be reported in the receiver error register,

induce a pulse on RERR, invoke the occurrence of

a RERR interrupt, and affect the current audio

sample according to the status of the HOLD bits.

The HOLD bits allow a choice of holding the previ-

ous sample, replacing the current sample with zero

(mute), or not changing the current audio sample.

If a mask bit is set to 0, the error is masked, which

implies the following: its occurrence will not be re-

ported in the receiver error register, will not induce

a pulse on RERR or generate a RERR interrupt,

and will not affect the current audio sample. The

QCRC and CCRC errors do not affect the current

audio sample, even if unmasked

6.4

Channel Status Data Handling

The first two bytes of the Channel Status block are

decoded into the Receiver Channel Status regis-

ter. The setting of the CHS bit in the Channel Sta-

tus Data Buffer Control register determines

whether the channel status decodes are from the A

channel (CHS = 0) or B channel (CHS = 1).

The PRO (professional) bit is extracted directly.

For consumer data, the COPY (copyright) bit is ex-

tracted, and the category code and L bits are de-

coded to determine SCMS status, indicated by the

ORIG (original) bit. If the category code is set to

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