AD7779 datasheet(54/97 Pages) AD

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AD7779

Data Sheet

Rev. 0 | Page 54 of 97

Daisy-Chain Mode

Daisy-chaining devices allows numerous devices to use the

same data interface lines by cascading the outputs of multiple

ADCs from separate AD7779 devices. In daisy-chain config-

uration, only one device has direct connection between the

DOUTx interface and the digital host. For the AD7779, daisy-

chain capability is implemented by cascading DOUT0 and DOUT1

through a number of devices, or by just using DOUT0 (this

depends on the selected DOUTx mode). The ability to daisy

chain devices and the limit on the number of devices that

can be handled by the chain is dependent on the selected

DOUTx mode and the decimation rate employed.

When operating in daisy-chain mode, it is required that all

AD7779 devices in the chain are correctly synchronized. See the

Digital Reset and Synchronization Pins section for more

information.

This feature is especially useful for reducing the component

count and wiring connections in, for example, isolated

multiconverter applications or for systems with a limited

interfacing capacity.

For daisy-chain operation, there are two different configurations

possible, as described in Table 37.

Using the DOUTx = 10 mode DOUT2 acts as input pins, as shown

in Figure 117. In this case, the DOUT0 pin of the AD7779 devices

is cascaded to the DOUT2 pin of the next device in the chain.

Data readback is analogous to clocking a shift register where

data is clocked on the rising edge of DCLK.

Table 37. DOUTx Modes in Daisy-Chain Operation

DOUT_FORMAT Bits/

FORMATx Pins

Number of DOUTx Lines Enabled

Associated Channels

DOUT0—Channel 0 to Channel 3 and DOUT2

DOUT1—Channel 4 to Channel 7 and DOUT3

DOUT2—input channel

DOUT3—input channel

DOUT0—Channel 0 to Channel 7 and DOUT2

DOUT2—Input Channel

U2 S0 CH0 TO CH7

U1 S0 CH0 TO CH7

U2 S0 CH0 TO CH7

U1 S0 CH0 TO CH7

U2 S1 CH0 TO CH7

U1 S1 CH0 TO CH7

U2 S1 CH0 TO CH7

U2 S3 CH0 TO CH7

U2 S0 CH0 TO CH7

U1 S1 CH0 TO CH7

U2 DOUT0

U1 DOUT2/DIN0

U1 DOUT0

U2 DOUT2/DIN0

DRDY

DCLK

DOUT2/DIN0

DOUT0

DOUT2/DIN0

DOUT0

Figure 117. Daisy-Chain Connection Mode, FORMAT0 = 1, FORMAT1 = 0 (S0 Means Sample 0 and S1 Means Sample 1); When Connected in Daisy-Chain Mode,

DOUT2 Acts as an Input Pin, Represented by DIN0

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