Datasheet

AD7983
Rev. A | Page 21 of 24
CHAIN MODE WITHOUT BUSY INDICATOR
This mode can be used to daisy-chain multiple AD7983s on a
3-wire serial interface. This feature is useful for reducing
component count and wiring connections, for example, in
isolated multiconverter applications or for systems with a
limited interfacing capacity. Data readback is analogous to
clocking a shift register.
A connection diagram example using two AD7983s is shown in
Figure 34, and the corresponding timing is given in Figure 35.
When SDI and CNV are low, SDO is driven low. With SCK low,
a rising edge on CNV initiates a conversion, selects the chain
mode, and disables the busy indicator. In this mode, CNV is
held high during the conversion phase and the subsequent data
readback. When the conversion is complete, the MSB is output
onto SDO and the AD7983 enters the acquisition phase and
goes into standby mode. The remaining data bits stored in the
internal shift register are clocked by subsequent SCK falling
edges. For each ADC, SDI feeds the input of the internal shift
register and is clocked by the SCK falling edge. Each ADC in
the chain outputs its data MSB first, and 16 × N clocks are
required to readback the N ADCs. 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 and, consequently, more AD7983s in the chain,
provided the digital host has an acceptable hold time. The
maximum conversion rate can be reduced due to the total
readback time.
DIGITAL HOST
CONVERT
CLK
DATA IN
AD7983
SDOSDI
CNV
A
SCK
AD7983
SDOSDI
CNV
B
SCK
06974-020
Figure 34. Chain Mode Without Busy Indicator Connection Diagram
t
CONV
t
CYC
t
SSDISCK
t
SCKL
t
SCK
t
HSDISCK
t
ACQ
A
CQUISITION
t
SSCKCNV
ACQUISITION
t
SCKH
CONVERSION
SDO
A
= SDI
B
t
HSCKCNV
SCK
CNV
SDI
A
= 0
SDO
B
t
EN
D
A
15 D
A
14 D
A
13
D
B
15 D
B
14 D
B
13 D
B
1D
B
0D
A
15 D
A
14 D
A
0D
A
1
D
A
1D
A
0
t
HSDO
123 15161714 18 30 31 32
t
DSDO
06974-021
Figure 35. Chain Mode Without Busy Indicator Serial Interface Timing