ADS1174IPAPR datasheet(21/39 Pages) TI1

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DAISY-CHAINING

SYNC

CLK

SYNC

DIN

DOUT1

SCLK

ADS1178

SYNC

DIN

CLK

DOUT1

DRDY

SerialDatafromDevices1and2

DRDY OutputfromDevice1

SCLK

ADS1178

DIN

CH1,U1

DOUT1

CH2,U1

CH3,U1

CH4,U1

CH5,U1

CH1,U2

CH2,U2

DIN2

SCLK

DRDY

(SPI)

FSYNC

(Frame-Sync)

129

130

145

146

257

258

ADS1174

ADS1178

www.ti.com ........................................................................................................................................ SBAS373B – OCTOBER 2007 – REVISED SEPTEMBER 2008

The maximum number of channels that may be

daisy-chained in this way is limited by the frequency

Multiple ADS1174/78s can be daisy-chained together

of fSCLK, the mode selection, and the CLKDIV input.

to simplify the serial interface connections. The

The frequency of fSCLK must be high enough to

DOUT1 data output pin of one ADS1174/78 is

completely shift the data out from all channels within

connected to the DIN input of the next ADS1174/78.

one fDATA period. Table 12 lists the maximum number

As Figure 21 illustrates, the DOUT1 pin of device 1

of daisy-chained channels when fSCLK = fCLK.

provides the output data to a controller, and the DIN

input of device 2 is grounded. Figure 22 describes the

data format when reading data back in a daisy-chain

configuration.

Figure 21. Daisy-Chaining of Two ADS1178s, SPI Protocol (FORMAT[2:0] = 000 or 001)

Figure 22. Daisy-Chain Data Format of Figure 21

Table 12. Maximum Channels in a Daisy-Chain (fSCLK = fCLK)

MODE SELECTION

CLKDIV

MAXIMUM NUMBER OF CHANNELS

High-Speed

160

Low-Power

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