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AD7693

Preliminary Technical Data

Rev. PrB | Page 22 of 24

CHAIN MODE WITH BUSY INDICATOR

This mode can also be used to daisy chain multiple AD7693s

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 AD7693s is shown

in Figure 43, and the corresponding timing is given in Figure 44.

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 AD7693 ADC labeled C in Figure 43) 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 AD7693 then enters the acquisition phase and powers

down. The data bits stored in the internal shift register are

clocked out, MSB first, 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 + 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 AD7693s in the

chain, provided the digital host has an acceptable hold time.

CLK

CONVERT

DATA IN

IRQ

DIGITAL HOST

CNV

SCK

SDO

SDI

CNV

SCK

SDO

SDI

CNV

SCK

SDO

SDI

AD7693

Figure 43. Chain Mode with Busy Indicator Connection Diagram

SDOA = SDIB

DA15 DA14 DA13

SCK

123

tEN

CONVERSION

ACQUISITION

tCONV

tCYC

tACQ

ACQUISITION

CNV = SDIA

DA1

415

tSCK

tSCKH

tSCKL

DA0

SDOB = SDIC

DB15 DB14 DB13

DA1

DB1DB0DA15 DA14

tSSDISCK

tHSDISC

tHSDO

tDSDO

SDOC

DC15 DC14 DC13

DA1DA0

DC1DC0DA14

DB1DB0DA15

DB15 DB14

tDSDOSDI

tSSCKCNV

tHSCKCNV

DA0

tDSDOSDI

Figure 44. Chain Mode with Busy Indicator Serial Interface Timing

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