EVAL-AD7764EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
EVAL-AD7764EBZ
Analog Devices
'EVAL-AD7764EBZ' PDF : 32 Pages View PDF
AD7764
DAISY CHAINING
Daisy chaining devices allows numerous devices to use the
same digital interface lines. This feature is especially useful for
reducing component count and wiring connections, such as
in isolated multiconverter applications or for systems with a
limited interfacing capacity. Data readback is analogous to
clocking a shift register.
The block diagram in Figure 40 shows how to connect devices
to achieve daisy-chain functionality. Figure 40 shows four
AD7764 devices daisy-chained together with a common
MCLK signal applied. This can only work in decimate 128× or
256× modes.
READING DATA IN DAISY-CHAIN MODE
Referring to Figure 40, note that the SDO line of AD7764 (A)
provides the output data from the chain of AD7764 converters.
Also, note that for the last device in the chain, AD7764 (D), the
SDI pin is connected to ground. All of the devices in the chain
must use common MCLK and SYNC signals.
To enable the daisy-chain conversion process, apply a common
SYNC pulse to all devices (see the Synchronization section).
After applying a SYNC pulse to all devices, the filter settling
time must pass before the FILTER-SETTLE bit is asserted
indicating valid conversion data at the output of the chain of
devices. As shown in Figure 41, the first conversion result is
output from the device labeled AD7764 (A). This 32-bit
conversion result is then followed by the conversion results
from the devices AD7764 (B), AD7764 (C), and AD7764 (D),
respectively with all conversion results output in an MSB first
sequence. The signals output from the daisy chain are the
stream of conversion results from the SDO pin of AD7764 (A)
and the FSO signal output by the first device in the chain,
AD7764 (A).
The falling edge of FSO signals the MSB of the first conversion
output in the chain. FSO stays logic low throughout the 32 SCO
clock periods needed to output the AD7764 (A) result and then
goes logic high during the output of the conversion results from
the devices AD7764 (B), AD7764 (C), and AD7764 (D).
The maximum number of devices that can be daisy-chained is
dependent on the decimation rate selected. Calculate the
maximum number of devices that can be daisy chained by
simply dividing the chosen decimation rate by 32 (the number
of bits that must be clocked out for each conversion). Table 12
provides the maximum number of chained devices for each
decimation rate.
Table 12. Maximum Chain Length for all Decimation Rates
Decimation Rate
Maximum Chain Length
256×
8
128×
4
64×
2
FSI
SYNC
MCLK
AD7764
(D)
FSI
SDI
SDO
SYNC
MCLK
AD7764
(C)
FSI
SDI
SDO
SYNC
MCLK
AD7764
(B)
FSI
SDI
SDO
SYNC
MCLK
AD7764
(A)
FSI
FSO
SDI
SYNC
SDO
MCLK
Figure 40. Daisy-Chaining Four Devices in Decimate 128× Mode Using a 40 MHz MCLK Signal
SCO
SDO (A)
FSO (A)
SDI (A) = SDO (B)
SDI (B) = SDO (C)
SDI (C) = SDO (D)
32 × tSCO
AD7764 (A)
32-BIT OUTPUT
32 × tSCO
AD7764 (B)
32-BIT OUTPUT
32 × tSCO
AD7764 (C)
32-BIT OUTPUT
32 × tSCO
AD7764 (D)
32-BIT OUTPUT
AD7764 (A)
32-BIT OUTPUT
AD7764 (B)
AD7764 (C)
AD7764 (D)
AD7764 (C)
AD7764 (D)
AD7764 (D)
Figure 41. Daisy-Chain Mode, Data Read Timing Diagram
(for Daisy-Chain Configuration Shown in Figure 40)
AD7764 (B)
AD7764 (C)
AD7764 (D)
AD7764 (B)
32-BIT OUTPUT
AD7764 (C)
AD7764 (D)
Rev. 0 | Page 23 of 32
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