CS6403 datasheet(16/54 Pages) CIRRUS

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Mode 2 (8-bit) Slave

Mode 2 (8-bit) provides a slaved SSI which may

be needed for 8-bit companded audio interfacing,

as is the case with many ISDN transceivers.

Mode 2 (8-bit) timing is similar to Mode 2 (16-

b it) timin g, bu t the serial d ata is 8-bit

companded, with the type of companding deter-

mined by the state of the UALAW pin. All 8

bits are used for audio, so no steering bit is nec-

essary, and consequently, no control information

can be transferred in this mode.

Mode 2 (8-bit) is selected by setting CONFIG

low, as opposed to high in Mode 2 (16-bit). See

Table 2 for more details. SCLK frequency is de-

t erm ined

t h e

S CLK_R ATE1

and

SCLK_RATE0 pins as given by Table 1. As in

Mode 2 (16-bit), the CS6403 will phase-lock to

the SCLK provided to it and derive its own tim-

ing from it.

Mode 2 (16-bit) Slave

Setting CONFIG high selects Mode 2 (16-bit).

When a DSP is connected to a CS6403 in

Mode 2 (16-bit), the DSP can reconfigure the

CS6403 by writing to the CS6403’s control reg-

isters via the SSI. To multiplex both data and

control on one serial interface, a steering bit is

used. The first bit sent (MSB) by the DSP deter-

mines whether a word is control or data, as

shown in Table 3.

If STR, the Steering Bit (b15), is zero, then the

data transferred on the Serial Interface is audio

data. Note that since a transfer typically consists

of 16 bits, this allows 15-bit precision for input

audio data. Output audio data remains in 16-bit

precision.

Companded audio data is treated differently than

16-bit data.

Input companded audio data has

eight zeroes followed by the 8-bit companded

data. Output companded audio data is formatted

such that 8-bit data is followed by eight zeroes.

If STR is one, the word transferred on the Serial

Interface is control information. If the RNW bit

is a zero, the word written by the external DSP

is stored by the CS6403 in the indicated destina-

tion register, and simultaneously, the state of the

destination register before the write is read back

into the DSP. If RNW is one, the data written

by the external DSP is ignored. The state of the

destination register is read back to the DSP.

Note that only one control word or one data

word may be transferred in a sample time, mean-

ing that no audio data is transferred in sample

times where control information is transferred. In

such sample times, the CS6403 will reuse (dou-

ble-sample) the audio data from the previous

sample time. As a result, to minimize distortion

of the audio signal, control transactions should

be made infrequently.

SCLK (in)

SSYNC (in)

SYNCOUT (out)

SDI (in)

b15 b14 b13 b12

SDO (out)

b15 b14 b13 b12

Figure 8. Serial Port Timing for Mode 2 (16-bit) - SLAVE

CS6403

DS192PP6

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