Datasheet

DVDD
BYPAS
1.65Vto3.6V
TieDVDDtoBYPASif
DVDDpoweris<2.25V.
OtherwisefloatBYPAS.
ADS1281
1 Fm
ADS1281
SCLK
DOUT1
DIN2
ADS1281
SCLK
DOUT2
FPGAorProcessor
DOUT1
DIN1
DRDY1
IRQ
SCLK(optional)
SCLK
DOUT2
DIN2
DRDY2
DIN2
IRQ(optional)
ADS1281
www.ti.com SBAS378D –AUGUST 2007–REVISED JUNE 2010
Serial Clock (SCLK)
DVDD POWER SUPPLY
The serial clock (SCLK) is an input that is used to
The DVDD supply operates over the range of +1.65V
clock data into (DIN) and out of (DOUT) the
to +3.6V. If DVDD is operated at less than 2.25V,
ADS1281. This input is a Schmitt-trigger input that
connect the DVDD pin to the BYPAS pin. If DVDD is
has a high degree of noise immunity. However, it is
greater than or equal to 2.25V, do not connect DVDD
recommended to keep SCLK as clean as possible to
to the BYPAS pin. Figure 43 shows this connection.
prevent possible glitches from inadvertently shifting
the data.
Data are shifted into DIN on the rising edge of SCLK
and data are shifted out of DOUT on the falling edge
of SCLK. If SCLK is held low for 64 DRDY cycles,
data transfer or commands in progress terminate and
the SPI interface resets. The next SCLK pulse starts
a new communication cycle. This timeout feature can
be used to recover the interface when a transmission
is interrupted or SCLK inadvertently glitches. SCLK
should remain low when not active.
Figure 43. DVDD Power
Data Input (DIN)
SERIAL INTERFACE
The data input pin (DIN) is used to input register data
and commands to the ADS1281. Keep DIN low when
A serial interface is used to read the conversion data
reading conversion data in the Read Data Continuous
and access the configuration registers. The interface
mode (except when issuing a STOP Read Data
consists of three basic signals: SCLK, DIN, and
Continuous command). Data on DIN are shifted into
DOUT. An additional output, DRDY, transitions low in
the converter on the rising edge of SCLK. In Pin
Read Data Continuous mode when data are ready for
mode, DIN is not used.
retrieval. Figure 44 shows the connection when
multiple converters are used.
Data Output (DOUT)
The data output pin (DOUT) is used to output data
from the ADS1281. Data are shifted out on DOUT on
the falling edge of SCLK. In Pin mode, only
conversion data are read from this pin.
Figure 44. Pin Mode Interface for Multiple
Devices
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