EVAL-AD7691SDZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7691SDZ' PDF : 28 Pages View PDF
Data Sheet
CHAIN MODE WITH BUSY INDICATOR
This mode can also be used to daisy-chain multiple AD7691
devices on a 3-wire serial interface while providing a busy
indicator. This feature is useful for reducing 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.
A connection diagram example using three AD7691 devices is
shown in Figure 45, and the corresponding timing is given in
Figure 46.
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. In this
mode, CNV is held high during the conversion phase and the
subsequent data readback. When all ADCs in the chain have
AD7691
completed their conversions, the SDO pin of the ADC closest to
the digital host (see the AD7691 ADC labeled C in Figure 45) is
driven high. This transition on SDO can be used as a busy
indicator to trigger the data readback controlled by the digital
host. The AD7691 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
readback the N ADCs. Although the rising edge can be used to
capture the data, a digital host using the SCK falling edge allows
a faster reading rate and, consequently, more AD7691 devices
in the chain, provided the digital host has an acceptable hold
time.
CNV
SDI AD7691 SDO
A
SCK
CNV
SDI AD7691 SDO
B
SCK
CNV
SDI AD7691 SDO
C
SCK
Figure 45. Chain Mode with Busy Indicator Connection Diagram
CONVERT
DIGITAL HOST
DATA IN
IRQ
CLK
CNV = SDIA
ACQUISITION
SCK
tHSCKCNV
SDOA = SDIB
SDOB = SDIC
SDOC
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
Figure 46. Chain Mode with Busy Indicator Serial Interface Timing
53 54 55
tDSDOSDI
tDSDOSDI
tDSDOSDI
DA1 DA0
Rev. E | Page 23 of 28
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