ADAQ7980 datasheet(39/49 Pages) AD

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Data Sheet

ADAQ7980/ADAQ7988

Rev. 0 | Page 39 of 49

3-WIRE CS MODE WITH THE BUSY INDICATOR

To connect a single ADAQ7980/ADAQ7988 to an SPI-compatible

digital host that has an interrupt input, use 3-wire CS mode

with the busy indicator.

Figure 73 shows the connection diagram, and Figure 74 shows

the corresponding timing.

With SDI tied to VIO, a rising edge on CNV initiates a conversion,

selects CS mode, and forces SDO to high impedance. SDO

stays in high impedance until the completion of the conversion

irrespective of the state of CNV. Prior to the minimum conversion

time, use CNV to select other SPI devices, such as analog

multiplexers; however, return CNV to low before the minimum

conversion time elapses and then hold it low for the maximum

conversion time to guarantee the generation of the busy signal

indicator.

When the conversion completes, SDO goes from high impedance

to low impedance. With a pull-up on the SDO line, use this

transition as an interrupt signal to initiate the data reading

controlled by the digital host. The ADAQ7980/ADAQ7988 then

enter the acquisition phase and power down. The data bits clock

out, MSB first, by subsequent SCK falling edges. The data is

valid on both SCK edges. Although the rising edge can capture the

data, a digital host using the SCK falling edge allows a faster

reading rate if it has an acceptable hold time. After the optional

17th SCK falling edge, or when CNV goes high, whichever is

earlier, SDO returns to high impedance.

If selecting multiple ADAQ7980/ADAQ7988 devices 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.

ADAQ7980/

ADAQ7988 SDO

SDI

DATA IN

IRQ

DIGITAL HOST

CONVERT

CLK

VIO

47kΩ

CNV

SCK

Figure 73. 3-Wire CS Mode with the Busy Indicator Connection Diagram

(SDI = 1, High)

tCONV

tCNVH

tCYC

ACQUISITION

tACQ

tSCK

tSCKH

tSCKL

CONVERSION

SCK

CNV

SDI = 1

SDO

D15

D14

tHSDO

tDSDO

tDIS

Figure 74. 3-Wire CS Mode with the Busy Indicator Serial Interface Timing (SDI = 1, High)

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