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EVAL-AD7985FMCZ View Datasheet(PDF) - Analog Devices

Part Name
Description
MFG CO.
EVAL-AD7985FMCZ
ADI
Analog Devices ADI
'EVAL-AD7985FMCZ' PDF : 28 Pages View PDF
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AD7985
Data Sheet
CS MODE, 4-WIRE WITH BUSY INDICATOR
This mode is usually used when a single AD7985 is connected
to an SPI-compatible digital host with an interrupt input and
when it is desired to keep CNV, which samples the analog input,
independent of the signal that selects the data reading. This
independence is particularly important in applications where
low jitter on CNV is desired. This mode is available only in normal
conversion mode (TURBO is low). The connection diagram is
shown in Figure 32, and the corresponding timing is given in
Figure 33.
With SDI high, a rising edge on CNV initiates a conversion,
selects CS mode, and forces SDO to high impedance. In this
mode, CNV must be held high during the conversion phase and
the subsequent data readback. (If SDI and CNV are low, SDO is
driven low.)
Prior to the minimum conversion time, SDI can select other SPI
devices, such as analog multiplexers, but SDI must be returned
low before the minimum conversion time elapses and then held
low for the maximum possible conversion time to guarantee the
generation of the busy signal indicator.
When the conversion is complete, SDO goes from high imped-
ance to low impedance. With a pull-up on the SDO line, this
transition can be used as an interrupt signal to initiate the data
readback controlled by the digital host. The AD7985 then enters
the acquisition phase and powers down. The data bits are then
clocked out, MSB first, by subsequent SCK falling edges. 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, provided that it has an accept-able hold
time. After the optional 17th SCK falling edge or when SDI goes
high (whichever occurs first), SDO returns to high impedance.
CS1
CONVERT
VIO
CNV
DIGITAL HOST
47kΩ
SDI AD7985 SDO
DATA IN
IRQ
SCK TURBO
CLK
Figure 32. CS Mode, 4-Wire with Busy Indicator Connection Diagram
TURBO = 0
CNV
ACQUISITION
tCONV
CONVERSION
tCYC
tACQ
ACQUISITION
(I/O QUIET
TIME)
tSSDICNV
SDI
tHSDICNV
SCK
SDO
tSCKL
tSCK
1
2
3
15
16
17
tHSDO
tSCKH
tDSDO
tEN
D15
D14
D1
D0
Figure 33. CS Mode, 4-Wire with Busy Indicator Serial Interface Timing
tQUIET
tDIS
Rev. C | Page 22 of 28
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