Datasheet

SCLK
DRDY
DOUT
Bit31 Bit30
Bit29
V
REF
2
>
V
REF
2
V
REF
2 (2 1)´ -
30
-V
REF
2 (2 1)´ -
30
-V
REF
2
2
30
2 1-
30
´
DRDY
DataUpdating
4/f
CLK
-V
REF
2
2
30
2 1-
30
´<
ADS1281
SBAS378D –AUGUST 2007–REVISED JUNE 2010 www.ti.com
Data Ready (DRDY)
DATA FORMAT
DRDY is an output; when it transitions low, this
The ADS1281 provides 32 bits of conversion data in
transition indicates new conversion data are ready, as
binary twos complement format, as shown in
shown in Figure 45. When reading data by the
Table 14. The LSB of the data is a redundant sign bit:
continuous mode, the data must be read within four
'0' for positive numbers and '1' for negative numbers.
CLK periods before DRDY goes low again or the data
However, when the output is clipped to +FS, the
are overwritten with new conversion data. When
LSB = 1; when the output is clipped to –FS, the
reading data by the command mode, the read
LSB = 0. If desired, the data readback may be
operation can overlap the occurrence of the next
stopped at 24 bits. Note that in sinc filter mode, the
DRDY without data corruption.
output data are scaled by 1/2.
Table 14. Ideal Output Code versus Input Signal
32-BIT IDEAL OUTPUT
CODE
(1)
INPUT SIGNAL V
IN
SINC
(AINP – AINN) FIR FILTER FILTER
(2)
7FFFFFFFh
(3)
Figure 45. DRDY with Data Retrieval
7FFFFFFEh 3FFFFFFFh
DRDY resets high on the first falling edge of SCLK.
00000002h 00000001h
Figure 45 and Figure 46 show the function of DRDY
with and without data readback, respectively.
0 00000000h 00000000h
If data are not retrieved (no SCLK provided), DRDY
pulses high for four f
CLK
periods during the update
FFFFFFFFh FFFFFFFFh
time, as shown in Figure 46.
80000001h C0000000h
80000000h
(3)
Figure 46. DRDY with No Data Retrieval
(1) Excludes effects of noise, linearity, offset, and gain errors.
(2) As a result of the reduction in oversampling ratio (OSR)
related to the sinc filter high data rates, the available
resolution may be reduced.
(3) In sinc filter mode, the output does not clip when the full-scale
range is exceeded.
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