EVAL-AD7982SDZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7982SDZ' PDF : 26 Pages View PDF
AD7982
CHAIN MODE WITH BUSY INDICATOR
Chain mode with busy indicator can also daisy-chain multiple
AD7982 devices on a 3-wire serial interface while providing a
busy indicator. This chain mode with 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 38 shows a connection diagram example using three
AD7982 devices, and Figure 39 shows the corresponding timing.
When SDI and CNV are low, SDO is driven low. With SCK
high, a rising edge on CNV initiates a conversion, selects the
chain mode, and enables the busy indicator feature.
Data Sheet
In this mode, CNV is held high during the conversion phase
and the subsequent data readback. When all ADCs in the chain
have completed their conversions, the SDO pin of the ADC
closest to the digital host (see the AD7982 ADC labeled C in
Figure 38) is driven high. The transition of driving the SDO pin
of the ADC to high can be used as a busy indicator to trigger the
data readback controlled by the digital host. The AD7982 then
enters the acquisition phase and powers down. The data bits
stored in the internal shift register are clocked out, MSB first,
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 + 1 clocks are required to read back the N ADCs.
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.
CONVERT
CNV
SDI AD7982 SDO
A
SCK
CNV
SDI AD7982 SDO
B
SCK
CNV
SDI AD7982 SDO
C
SCK
DIGITAL HOST
DATA IN
IRQ
CNV = SDIA
ACQUISITION
SCK
tHSCKCNV
SDOA = SDIB
SDOB = SDIC
SDOC
CLK
Figure 38. Chain Mode with Busy Indicator Connection Diagram
tCYC
tCONV
CONVERSION
tSSCKCNV
tEN
tDSDOSDI
tDSDOSDI
tACQ
ACQUISITION
tSCKH
tSCK
1
2
3
4
17 18 19 20 21
tSSDISCK
tHSDISCK
tSCKL
35 36 37 38 39
DA17 DA16 DA15
tHSDO
tDSDO
DA1 DA0
DB17 DB16 DB15
DB1 DB0 DA17 DA16
DA1 DA0
DC17 DC16 DC15
DC1 DC0 DB17 DB16
DB1 DB0 DA17 DA16
53 54 55
tDSDOSDI
tDSDOSDI
tDSDOSDI
DA1 DA0
Figure 39. Chain Mode with Busy Indicator Serial Interface Timing
Rev. E | Page 24 of 26
Share Link: 
