EVAL-AD7982SDZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7982SDZ' PDF : 26 Pages View PDF
Data Sheet
CHAIN MODE WITHOUT BUSY INDICATOR
Chain mode without busy indicator can be used to daisy-chain
multiple AD7982 devices on a 3-wire serial interface. The chain
mode without busy indicator feature reduces component count
and wiring connections, for example, in isolated multiconverter
applications or for systems with a limited interfacing capacity.
Data readback is analogous to clocking a shift register.
Figure 36 shows a connection diagram example using two AD7982
devices, and Figure 37 shows the corresponding timing.
When SDI and CNV are low, SDO is driven low. With SCK low, a
rising edge on CNV initiates a conversion, selects the chain mode,
and disables the busy indicator.
In this mode, CNV is held high during the conversion phase and
the subsequent data readback.
AD7982
When the conversion completes, the MSB is output onto SDO
and the AD7982 enters the acquisition phase and powers down.
The remaining data bits stored in the internal shift register are
clocked by subsequent SCK falling edges. For each ADC, SDI
feeds the input of the internal shift register and is clocked by
the SCK falling edge. Each ADC in the chain outputs its data
MSB first, and 18 × N clocks are required to read back the N
ADCs. The data is valid on both SCK edges. Although the
rising edge can capture the data, a digital host using the SCK
falling edge allows a faster reading rate and consequently more
AD7982 devices in the chain, provided the digital host has an
acceptable hold time. The maximum conversion rate can be
reduced due to the total readback time.
SDIA = 0
CNV
ACQUISITION
SCK
tHSCKCNV
SDOA = SDIB
SDOB
CONVERT
CNV
SDI AD7982 SDO
A
SCK
CNV
SDI AD7982 SDO
B
SCK
DIGITAL HOST
DATA IN
CLK
Figure 36. Chain Mode Without Busy Indicator Connection Diagram
tCYC
tCONV
tACQ
CONVERSION
ACQUISITION
tSSCKCNV
tSCKL
tSCK
1
2
3
16
17
18
19
20
34
tSSDISCK
tSCKH
tEN
tHSDISCK
DA17 DA16 DA15
DA1
DA0
tHSDO
tDSDO
DB17 DB16 DB15
DB1
DB0 DA17 DA16
Figure 37. Chain Mode Without Busy Indicator Serial Interface Timing
35
36
DA1
DA0
Rev. E | Page 23 of 26
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