ad7688brm Analog Devices, Inc., ad7688brm Datasheet - Page 19

• Manufacturer Part Number: ad7688brm
• Description: 16-bit, 1.5 Lsb Inl, 500 Ksps Pulsar? Differential Adc In Msop/qfn
• Manufacturer: Analog Devices, Inc.

CS MODE 4-WIRE, NO BUSY INDICATOR
This mode is usually used when multiple AD7688s are
connected to an SPI-compatible digital host.
A connection diagram example using two AD7688s is shown in
Figure 38 and the corresponding timing is given in Figure 39.
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 could
be used to select other SPI devices, such as analog multiplexers,
SDI(CS1)
SDI(CS2)
ACQUISITION
SDO
CNV
SCK
t
SSDICNV
t
HSDICNV
CONVERSION
t
CONV
t
EN
SDI
AD7688
CNV
SCK
D15
1
t
HSDO
Figure 39. CS Mode 4-Wire, No BUSY Indicator Serial Interface Timing
Figure 38. CS Mode 4-Wire, No BUSY Indicator Connection Diagram
SDO
D14
2
D13
3
t
DSDO
t
SCKL
t
SCKH
14
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SDI
t
SCK
AD7688
15
D1
CNV
SCK
t
CYC
but SDI must be returned high before the minimum conversion
time and held high until the maximum conversion time to
avoid the generation of the BUSY signal indicator. When the
conversion is complete, the AD7688 enters the acquisition
phase and powers down. Each ADC result can be read by
bringing low its SDI input 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 AD7688 can be read.
16
D0
ACQUISITION
SDO
t
ACQ
D15
17
CS2
CS1
CONVERT
DATA IN
CLK
DIGITAL HOST
D14
18
30
31
D1
32
D0
AD7688
t
DIS