Datasheet

AD7691 Data Sheet
Rev. C | Page 18 of 28
CS MODE, 3-WIRE WITHOUT BUSY INDICATOR
This mode is usually used when a single AD7691 is connected
to an SPI-compatible digital host. The connection diagram is
shown in Figure 35, and the corresponding timing is given in
Figure 36.
With SDI tied to VIO, a rising edge on CNV initiates a
conversion, selects the
CS
mode, and forces SDO to high
impedance. Once a conversion is initiated, it continues until
completion irrespective of the state of CNV. This can be useful,
for instance, to bring CNV low to select other SPI devices, such
as analog multiplexers, but CNV must be returned high before
the minimum conversion time elapses and then held high for
the maximum possible conversion time to avoid the generation
of the busy signal indicator. When the conversion is complete,
the AD7691 enters the acquisition phase and powers down.
When CNV goes low, the MSB is output onto SDO. The
remaining data bits are clocked by subsequent SCK falling
edges. The data is valid on both SCK edges. Although the rising
edge can be used to capture the data, a digital host using the
SCK falling edge can allow a faster reading rate, provided it has
an acceptable hold time. After the 18
th
SCK falling edge, or
when CNV goes high, whichever occurs first, SDO returns to
high impedance.
CNV
SCK
SDOSDI
DATA IN
CLK
CONVERT
V
IO
DIGITAL HOST
AD7691
06146-011
Figure 35. 3-Wire
CS
Mode Without Busy Indicator
Connection Diagram (SDI High)
SDO
D17 D16 D15 D1 D0
t
DIS
SCK
123 161718
t
SCK
t
SCKL
t
SCKH
t
HSDO
t
DSDO
CNV
CONVERSIONACQUISITION
t
CONV
t
CYC
ACQUISITION
SDI = 1
t
CNVH
t
ACQ
t
EN
06146-012
Figure 36. 3-Wire
CS
Mode Without Busy Indicator Serial Interface Timing (SDI High)