Datasheet

DAISY-CHAINING
SYNC
CLK
SYNC
DIN DOUT1
SCLK SCLK
ADS1178
SYNC
DIN
CLK CLK
DOUT1
DRDY
SerialDatafromDevices1and2
DRDY OutputfromDevice1
SCLK
ADS1178
U2
U1
DIN
CH1,U1DOUT1 CH2,U1 CH3,U1 CH4,U1 CH5,U1 CH1,U2 CH2,U2 DIN2
SCLK
DRDY
(SPI)
FSYNC
(Frame-Sync)
1 2
17 3318 34 49 50 65 66 129 130 145 146 257 258
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 f
SCLK
, the mode selection, and the CLKDIV input.
to simplify the serial interface connections. The
The frequency of f
SCLK
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 f
DATA
period. Table 12 lists the maximum number
As Figure 21 illustrates, the DOUT1 pin of device 1
of daisy-chained channels when f
SCLK
= f
CLK
.
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 (f
SCLK
= f
CLK
)
MODE SELECTION CLKDIV MAXIMUM NUMBER OF CHANNELS
1 32
High-Speed
0 16
1 160
Low-Power
0 32
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