AD1835AS datasheet(21/23 Pages) AD

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PRELIMINARY TECHNICAL DATA

AD1835

–21–

CASCADE MODE

Dual AD1835Cascade

The AD1835 can be cascaded to an additional AD1835 that,

in addition to six external stereo ADCs, can be used to create a

32-channel audio system with 16 inputs and 16 outputs. The

cascade is designed to connect to a SHARC DSP and operates

in a time division multiplexing (TDM) format. Figure 14

shows the connection diagram for cascade operation. The digital

interface for both parts must be set to operate in Auxiliary

512 mode by programming ADC Control Register II. AD1835

#1 is set as a master device by connecting the

M/S pin to DGND,

and AD1835 #2 is set as a slave device by connecting the

M/S to

DVDD. Both devices should be run from the same MCLK and

PD/RST signals to ensure that they are synchronized.

With Device 1 set as a master, it will generate the frame-sync and

bit clock signals. These signals are sent to the SHARC and

Device 2 ensuring that both know when to send and receive data.

The cascade can be thought of as two 256-bit shift registers,

one for each device. At the beginning of a sample interval, the

shift registers contain the ADC results from the previous sample

interval. The first shift register (Device 1) clocks data into the

SHARC and also clocks in data from the second shift register

(Device 2). While this is happening, the SHARC is sending

DAC data to the second shift register. By the end of the sample

interval, all 512 bits of ADC data in the shift registers will have

been clocked into the SHARC and been replaced by DAC data

which is subsequently written to the DACs. Figure 15 shows

the timing diagram for the cascade operation.

AUX ADC

(SLAVE)

ALRCLK

ABCLK

ASDATA

DSDATA

ALRCLK

ABCLK

ASDATA

DSDATA

AD1835 #1

(MASTER)

AD1835 #2

(SLAVE)

SHARC

(SLAVE)

AUX ADC

(SLAVE)

AUX ADC

(SLAVE)

AUX ADC

(SLAVE)

AUX ADC

(SLAVE)

AUX ADC

(SLAVE)

DRx

RFSx

RCLKx

TCLKx

DTx

TFSx

Figure 14. Cascade

AD1835 #1 DACs

AD1835 #2 DACs

TFSx/

RFSx

DTx

AD1835 #1 ADCs

AD1835 #2 ADCs

DRx

256 ABCLKs

MSB

MSB-1

LSB

32 ABCLKs

ABCLK

DTx

MSB

MSB-1

LSB

DRx

DON’T CARE

Figure 15. Cascade Timing

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