Datasheet

AD7690
Rev. B | Page 17 of 24
CS MODE, 3-WIRE WITHOUT BUSY INDICATOR
This mode is usually used when a single AD7690 is connected
to an SPI-compatible digital host. The connection diagram is
shown in Figure 34, and the corresponding timing is given in
Figure 35.
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; however, 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 AD7690 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 allows 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
AD7690
05792-011
Figure 34. 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
05792-012
Figure 35. 3-Wire
CS
Mode Without Busy Indicator Serial Interface Timing (SDI High)