EVAL-AD7982SDZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7982SDZ' PDF : 26 Pages View PDF
AD7982
CS MODE, 3-WIRE WITH BUSY INDICATOR
CS mode, 3-wire with busy indicator is usually used when a
single AD7982 is connected to an SPI-compatible digital host
having an interrupt input.
The connection diagram is shown in Figure 30, and the
corresponding timing is given in Figure 31.
With SDI tied to VIO, a rising edge on CNV initiates a
conversion, selects the CS mode, and forces SDO to high
impedance. SDO is maintained in high impedance until the
completion of the conversion irrespective of the state of CNV.
Prior to the minimum conversion time, CNV can be used to
select other SPI devices, such as analog multiplexers, but CNV
must be returned low before the minimum conversion time
elapses and then held low for the maximum possible
conversion time to guarantee the generation of the busy signal
indicator.
Data Sheet
When the conversion completes, SDO goes from high impedance
to low impedance. With a pull-up resistor on the SDO line, the
high impedance to low impedance transition can be used as an
interrupt signal to initiate the data reading controlled by the digital
host. The AD7982 then enters the acquisition phase and powers
down. The data bits are then clocked out, MSB first, 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 optional 19th SCK falling edge
or when CNV goes high (whichever occurs first), SDO returns to
high impedance.
If multiple AD7982 devices are selected at the same time, the
SDO output pin handles this contention without damage or
induced latch-up. Meanwhile, it is recommended to keep this
contention as short as possible to limit extra power dissipation.
VIO
SDI
CNV
AD7982
SDO
CONVERT
VIO
DIGITAL HOST
47kΩ
DATA IN
SDI = 1
tCNVH
CNV
SCK
IRQ
CLK
Figure 30. CS Mode, 3-Wire with Busy Indicator Connection Diagram (SDI High)
tCYC
tCONV
tACQ
ACQUISITION
CONVERSION
SCK
SDO
ACQUISITION
tSCKL
tSCK
1
2
3
17
18
19
tHSDO
tSCKH
tDSDO
tDIS
D17
D16
D1
D0
Figure 31. CS Mode, 3-Wire with Busy Indicator Serial Interface Timing (SDI High)
Rev. E | Page 20 of 26
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