AD7656ABSTZ datasheet(22/29 Pages) AD

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Data Sheet

AD7656A

DOUT A

DOUT B

SCLK

Figure 27. Serial Interface with Two DOUT x Lines

BUSY

ACQUISITION

CONVERSION

ACQUISITION

SCLK

DOUT A,

DOUT B,

DOUT C

DB15

DB14

DB13

DB1

DB0

tACQ

t10

tCONVERT

tQUIET

t21

t20

t17

t16

t18

t19

CONVST A,

CONVST B,

CONVST C

Figure 28. Serial Read Operation

DIGITAL HOST

CONVERT

SCLK

AD7656A

CONVST x

SCLK

DATA IN1

DATA IN2

DOUT A

DOUT B

DOUT A

DOUT B

DCIN A

DCIN B

DCEN = 1

DEVICE 1

DCEN = 0

DEVICE 2

Figure 29. Daisy-Chain Configuration

SERIAL READ OPERATION

Figure 28 shows the timing diagram for reading data from the

AD7656A serial interface. The SCLK input signal provides the

clock source for the serial interface. The CS signal goes low to

access data from the AD7656A. The falling edge of CS takes

the bus out of a three-state condition and clocks out the MSB of

the 16-bit conversion result. The ADCs output 16 bits for each

conversion result; the data stream of the AD7656A consists of

16 bits of conversion data provided MSB first.

The first bit of the conversion result is valid on the first SCLK

falling edge after the CS falling edge. The subsequent 15 data

bits are clocked out on the rising edge of the SCLK signal. Data

is valid on the SCLK falling edge. To access each conversion result,

provide 16 clock pulses to the AD7656A. Figure 28 shows how a

16-SCLK read is used to access the conversion results.

DAISY-CHAIN MODE (DCEN = 1, SER/PAR/SEL = 1)

When reading conversion data back from the AD7656A using

their three, two, and one DOUT x pins, it is possible to configure

the device to operate in daisy-chain mode using the DCEN pin.

This daisy-chain feature allows multiple AD7656A devices to be

cascaded together and is useful for reducing the component

count and wiring connections. An example connection of two

devices is shown in Figure 29. This configuration shows the use

of two DOUT x lines. Simultaneous sampling of the 12 analog

inputs is possible by using a common CONVST x signal. The

DB5, DB4, and DB3 pins are used as the DCIN A to DCIN C data

input pins for the daisy-chain mode.

Rev. 0 | Page 21 of 28

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