AD7915 datasheet(21/26 Pages) AD

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Data Sheet

AD7915/AD7916

Rev. 0 | Page 21 of 26

CHAIN MODE, WITHOUT BUSY INDICATOR

This mode can be used to daisy-chain multiple AD7915/

AD7916 devices 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 AD7915/AD7916

devices is shown in Figure 43, and the corresponding timing is

given in Figure 44.

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

low, a rising edge on CNV initiates a conversion, and selects the

chain mode. 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

AD7915/AD7916 enter the acquisition phase and power down.

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 register and is clocked by the

SCK falling edge. Each ADC in the chain outputs its data MSB

first, and 16 × N clocks are required to read back 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

AD7915/AD7916 devices in the chain, provided that the digital

host has an acceptable hold time. The maximum conversion rate

may be reduced due to the total readback time.

CONVERT

DATA IN

CLK

DIGITAL HOST

AD7915/

AD7916

SDO

CNV

SCK

AD7915/

AD7916

SDO

CNV

SCK

SDI/CS

Figure 43. Chain Mode Without Busy Indicator Connection Diagram

DA15

DA14

DA13

SCK

tSSDISCK

tHSDISCK

tEN

CONVERSION

ACQUISITION

tCONV

tCYC

tACQ

ACQUISITION

CNV

DA1

tSCK

tSCKL

tSCKH

DA0

SDOB

DB15

DB14

DB13

DA1

DB1DB0DA15

DA14

tHSDO

tDSDO

tSSCKCNV

tHSCKCNV

DA0

SDI/CSA = 0

SDOA = SDI/CSB

Figure 44. Chain Mode Without Busy Indicator Serial Interface Timing

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