EVAL-AD7985FMCZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7985FMCZ' PDF : 28 Pages View PDF
AD7985
Data Sheet
CS MODE, 3-WIRE WITH BUSY INDICATOR
This mode is usually used when a single AD7985 is connected
to an SPI-compatible digital host that has an interrupt input. It
is available only in normal conversion mode (TURBO is low).
The connection diagram is shown in Figure 28, and the corre-
sponding timing is given in Figure 29.
With SDI tied to VIO, a rising edge on CNV initiates a conversion,
selects CS mode, and forces SDO to high impedance. SDO
is maintained in high impedance until the completion of the
conversion, irrespective of the state of CNV. Prior to the minimum
conversion time, CNV can select other SPI devices, such as analog
multiplexers, but CNV 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 acceptable hold time.
After the optional 17th SCK falling edge, SDO returns to high
impedance.
If multiple AD7985 devices are selected at the same time, the
SDO output pin handles this contention without damage or
induced latch-up. Meanwhile, it is recommended that this
contention be kept as short as possible to limit extra power
dissipation.
CONVERT
CNV
VIO
VIO
DIGITAL HOST
47kΩ
SDI AD7985 SDO
DATA IN
IRQ
SCK TURBO
CLK
Figure 28. CS Mode, 3-Wire with Busy Indicator Connection Diagram (SDI High)
TURBO = 0
SDI = 1
tCNVH
CNV
ACQUISITION
tCONV
CONVERSION
SCK
SDO
tCYC
tACQ
ACQUISITION
tSCKL
tSCK
1
2
tHSDO
3
15
16
tDSDO
tSCKH
D15
D14
D1
(I/O QUIET
TIME)
tQUIET
17
tDIS
D0
Figure 29. CS Mode, 3-Wire with Busy Indicator Serial Interface Timing (SDI High)
Rev. C | Page 20 of 28
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