Datasheet

AD7983
Rev. A | Page 19 of 24
CS MODE, 4-WIRE WITHOUT BUSY INDICATOR
This mode is usually used when multiple AD7983s are
connected to an SPI-compatible digital host.
A connection diagram example using two AD7983s is shown in
Figure 30, and the corresponding timing is given in Figure 31.
With SDI high, a rising edge on CNV initiates a conversion,
selects the
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 be
used to select other SPI devices, such as analog multiplexers,
but SDI must be returned high before the minimum conversion
time elapses and then held high for the maximum conversion
time to avoid the generation of the busy signal indicator.
When the conversion is complete, the AD7983 enters the
acquisition phase and goes into standby mode. Each ADC result
can be read by bringing its SDI input low, which consequently
outputs the MSB onto SDO. The remaining data bits are then
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
16th SCK falling edge or when SDI goes high, whichever is
earlier, SDO returns to high impedance and another AD7983
can be read.
DIGITAL HOST
CONVERT
CS2
CS1
CLK
DATA IN
AD7983
SDOSDI
CNV
SCK
AD7983
SDOSDI
CNV
SCK
06974-016
Figure 30.
CS
Mode, 4-Wire Without Busy Indicator Connection Diagram
t
CONV
t
CYC
ACQUISITION
ACQUISITION
t
ACQ
t
SCK
t
SCKH
t
SCKL
CONVERSION
SCK
CNV
t
SSDICNV
t
HSDICNV
SDO
D15 D13D14 D1 D0 D15 D14 D1
D0
t
HSDO
t
EN
1 2 3 14 15 16 17 18 30 31 32
t
DSDO
t
DIS
SDI(CS1)
SDI(CS2)
06974-017
Figure 31.
CS
Mode, 4-Wire Without Busy Indicator Serial Interface Timing