ADS1274IPAPR datasheet(33/51 Pages) TI1

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CH1

DOUT1

CH2

DOUT2

CH3

DOUT3

CH4

DOUT4

SCLK

DRDY

(SPI)

FSYNC

(Frame-Sync)

CH5

DOUT5

CH6

DOUT6

CH7

DOUT7

CH8

DOUT8

ADS1278 Only

ADS1274

ADS1278

www.ti.com

SBAS367F

– JUNE 2007 – REVISED FEBRUARY 2011

Figure 80. Discrete Data Output Mode

Table 15. Maximum Channels in a Daisy-Chain

DAISY-CHAINING

(fSCLK = fCLK)

Multiple ADS1274/78s can be daisy-chained together

MAXIMUM NUMBER

to output data on a single pin. The DOUT1 data

MODE SELECTION

CLKDIV

OF CHANNELS

output pin of one device is connected to the DIN of

High-Speed

the next device. As shown in Figure 81, the DOUT1

High-Resolution

pin of device 1 provides the output data to a

controller, and the DIN of device 2 is grounded.

Low-Power

Figure 82 shows the data format when reading back

data.

106

Low-Speed

The maximum number of channels that may be

daisy-chained in this way is limited by the frequency

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

Whether the interface protocol is SPI or Frame-Sync,

The frequency of fSCLK must be high enough to

it is recommended to synchronize all devices by tying

completely shift the data out from all channels within

the SYNC inputs together. When synchronized in SPI

one fDATA period. Table 15 lists the maximum number

protocol, it is only necessary to monitor the DRDY

of daisy-chained channels when fSCLK = fCLK.

output of one ADS1274/78.

To increase the number of data channels possible in

In Frame-Sync interface protocol, the data from all

a chain, a segmented DOUT scheme may be used,

devices are ready after the rising edge of FSYNC.

producing two data streams. Figure 83 illustrates four

Since DOUT1 and DIN are both shifted on the falling

ADS1274/78s,

with

pairs

ADS1274/78s

edge of SCLK, the propagation delay on DOUT1

daisy-chained together. The channel data of each

creates a setup time on DIN. Minimize the skew in

daisy-chained pair are shifted out in parallel and

SCLK to avoid timing violations.

received by the processor through independent data

channels.

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ADS1274IPAPR Datasheet(PDF) 33 Page - Texas Instruments

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