AD7983 datasheet(21/24 Pages) AD

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AD7983

Rev. 0 | Page 21 of 24

CHAIN MODE WITHOUT BUSY INDICATOR

This mode can be used to daisy-chain multiple AD7983s on a

3-wire serial interface. 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 two AD7983s is shown in

Figure 34, and the corresponding timing is given in Figure 35.

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

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

mode, and disables the busy indicator. In this mode, CNV is

held high during the conversion phase and the subsequent data

readback. When the conversion is complete, the MSB is output

onto SDO and the AD7983 enters the acquisition phase and

goes into standby mode. The remaining data bits stored in the

internal shift register are clocked by subsequent SCK falling

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

the chain outputs its data MSB first, and 16 × N clocks are

required to readback the N ADCs. 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 and, consequently, more AD7983s in the chain,

provided the digital host has an acceptable hold time. The

maximum conversion rate can be reduced due to the total

readback time.

DIGITAL HOST

CONVERT

CLK

DATA IN

AD7983 SDO

SDI

CNV

SCK

AD7983 SDO

SDI

CNV

SCK

Figure 34. Chain Mode Without Busy Indicator Connection Diagram

tCONV

tCYC

tSSDISCK

tSCKL

tSCK

tHSDISCK

tACQ

ACQUISITION

tSSCKCNV

ACQUISITION

tSCKH

CONVERSION

SDOA = SDIB

tHSCKCNV

SCK

CNV

SDIA = 0

SDOB

tEN

DA15

DA14

DA13

DB15

DB14

DB13

DB1DB0DA15

DA14

DA0

DA1

DA1DA0

tHSDO

tDSDO

Figure 35. Chain Mode Without Busy Indicator Serial Interface Timing

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