AD7944BCPZ datasheet(24/28 Pages) AD

24 / 28 page

AD7944

Rev. 0 | Page 24 of 28

CHAIN MODE WITH BUSY INDICATOR

This mode can be used to daisy-chain multiple AD7944 devices

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

is available only in normal conversion mode (TURBO low).

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 AD7944 devices 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 chain mode,

and enables the busy indicator. 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 AD7944

ADC labeled C in Figure 36) is driven high. This transition on

SDO can be used as a busy indicator to trigger the data read-

back controlled by the digital host. The AD7944 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 14 × N + 1 clocks

are required to read back 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

AD7944 devices in the chain, provided that the digital host has

an acceptable hold time.

CONVERT

DATA IN

CLK

DIGITAL HOST

AD7944

SDI

SDO

CNV

SCK

AD7944

SDI

SDO

CNV

SCK

IRQ

AD7944

SDI

SDO

CNV

SCK

TURBO

SDOA = SDIB

SCK

Figure 36. Chain Mode with Busy Indicator Connection Diagram

DA13 DA12 DA11

tEN

CONVERSION

ACQUISITION

tCONV

tACQ

ACQUISITION

tCYC

CNV = SDIA

DA1

413

tSCK

tSCKH

tSCKL

DA0

SDOB = SDIC

DB13 DB12 DB11

DA1

DB1DB0DA13 DA12

tSSDISCK

tHSDISCK

tHSDO

tDSDO

SDOC

DC13 DC12 DC11

DA1DA0

DC1DC0DA12

DB1DB0DA13

DB13 DB12

tDSDOSDI

tHSCKCNV

DA0

tDSDOSDI

URBO = 0

tSSCKCNV

Figure 37. Chain Mode with Busy Indicator Serial Interface Timing

AD7944BCPZ датащи(PDF) 24 Page - Analog Devices

AD7944BCPZ датащи(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL