AD7983BCPZ-R2 datasheet(23/25 Pages) AD

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AD7983

Data Sheet

Rev. B | Page 22 of 24

CHAIN MODE WITH BUSY INDICATOR

This mode can also be used to daisy-chain multiple AD7983s

on a 3-wire serial interface while providing a busy indicator.

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 three AD7983s is shown

in Figure 36, and the corresponding timing is given in Figure 37.

When SDI and CNV are low, SDO is driven low. With SCK

high, a rising edge on CNV initiates a conversion, selects the

chain mode, and enables the busy indicator feature. In this

mode, CNV is held high during the conversion phase and the

subsequent data readback. When all ADCs in the chain have

completed their conversions, the SDO pin of the ADC closest

to the digital host (see the AD7983 ADC labeled C in Figure 36)

is driven high. This transition on SDO can be used as a busy

indicator to trigger the data readback controlled by the digital

host. The AD7983 then enters the acquisition phase and goes

into standby mode. The data bits stored in the internal shift

edges. For each ADC, SDI feeds the input of the internal shift

chain outputs its data MSB first, and 16 × N + 1 clocks are required

to readback the N ADCs. 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.

AD7983

SDO

SDI

DATA IN

IRQ

DIGITAL HOST

CONVERT

CLK

CNV

SCK

AD7983

SDO

SDI

CNV

SCK

AD7983

SDO

SDI

CNV

SCK

Figure 36. Chain Mode with Busy Indicator Connection Diagram

tCONV

tCYC

tSSDISCK

tSCKH

tSCK

tHSDISCK

tACQ

tDSDOSDI

tDSDODSI

ACQUISITION

tSSCKCNV

ACQUISITION

tSCKL

CONVERSION

tHSCKCNV

SCK

CNV = SDIA

SDOA = SDIB

SDOB = SDIC

SDOC

tEN

DA15

DA14

DA13

DB15

DB14

DB13

DC15

DC14

DC13

DB1DB0DA15

DA14

DA1DA0

DC1DC0DB15

DB14

DA0

DA1

DB0

DB1DA14

DA15

DA1DA0

tHSDO

333435

tDSDO

tDSDOSDI

Figure 37. Chain Mode with Busy Indicator Serial Interface Timing

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