AD7771_17 Datasheet, PDF (59/99 Pages) Analog Devices – 8-Channel, 24-Bit, Simultaneous Sampling ADC

AD7771
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 AD7771 devices. In daisy-chain configura-
tion, only one device has a direct connection between the
DOUTx interface and the digital host. For the AD7771, daisy-
chain capability is implemented by cascading DOUT0 and DOUT1
through a number of devices, or by just using DOUT0 (the
number of DOUTx pins available 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
AD7771 devices in the chain are correctly synchronized. See
Table 37. DOUTx Modes in Daisy-Chain Operation
DOUT_FORMAT Bits/
FORMATx Pins
Number of DOUTx Lines Enabled
01
2
10
1
Data Sheet
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 FORMATx = 10 mode, DOUT2 acts as an input pin, as
shown in Figure 136. In this case, the DOUT0 pin of the AD7771
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.
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
DOUT2/DIN0
DOUT0
U2
DOUT2/DIN0
DOUT0
DCLK
DRDY
U2 DOUT2/DIN0
U2 DOUT0
0
0
0
0
0
U2 S0 CH0 TO CH7
0
U2 S1 CH0 TO CH7
0
U2 S0 CH0 TO CH7
U1 DOUT2/DIN0
U2 S0 CH0 TO CH7 U2 S0 CH0 TO CH7 U2 S1 CH0 TO CH7 U2 S1 CH0 TO CH7 U2 S0 CH0 TO CH7
U1 DOUT0
U1 S0 CH0 TO CH7 U1 S0 CH0 TO CH7 U1 S1 CH0 TO CH7 U2 S3 CH0 TO CH7 U1 S1 CH0 TO CH7
Figure 136. 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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