EVAL-AD7980SDZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7980SDZ' PDF : 28 Pages View PDF
AD7980
CHAIN MODE WITHOUT BUSY INDICATOR
This mode can be used to daisy-chain multiple AD7980 devices
on a 3-wire serial interface. This feature is useful for reducing
component count and wiring connections, for example, in
isolated multi-converter applications or for systems with a
limited interfacing capacity. Data readback is analogous to
clocking a shift register.
A connection diagram example using two AD7980s is shown in
Figure 39, and the corresponding timing is given in Figure 40.
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
Data Sheet
readback. When the conversion is complete, the MSB is output
onto SDO and the AD7980 enters the acquisition phase and
powers down. 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 AD7980 devices in the chain,
provided the digital host has an acceptable hold time. The
maximum conversion rate may be reduced due to the total
readback time.
CNV
SDI AD7980 SDO
A
SCK
CNV
SDI AD7980 SDO
B
SCK
CONVERT
DIGITAL HOST
DATA IN
CLK
SDIA = 0
CNV
AQUISITION
SCK
tHSCKCNV
SDOA = SDIB
SDOB
tCONV
CONVERSION
tSSCKCNV
tEN
Figure 39. Chain Mode Without Busy Indicator Connection Diagram
tCYC
tACQ
tSCKL
AQUISITION
tSCK
1
2
3
14
15
16
17
18
30
tSSDISCK
tHSDISC
tSCKH
DA15
tHSDO
DB15
DA14 DA13
tDSDO
DB14 DB13
DA1
DA0
DB1
DB0 DA15 DA14
Figure 40. Chain Mode Without Busy Indicator Serial Interface Timing
31
32
DA1
DA0
Rev. F | Page 22 of 26
Share Link: 
