Information

BMA280
Data sheet
Page 18
BST-BMA280-DS000-11 | Revision 1.8 | August 2014 Bosch Sensortec
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Note: Specifications within this document are subject to change without notice.
4.3 Sensor data
4.3.1 Acceleration data
The width of acceleration data is 14 bits given in two´s complement representation. The 14 bits
for each axis are split into an MSB upper part (one byte containing bits 13 to 6) and an LSB
lower part (one byte containing bits 5 to 0 of acceleration and a (0x02, 0x04, 0x06) new_data
flag). Reading the acceleration data registers shall always start with the LSB part. In order to
ensure the integrity of the acceleration data, the content of an MSB register is locked by reading
the corresponding LSB register (shadowing procedure). When shadowing is enabled, the MSB
must always be read in order to remove the data lock. The shadowing procedure can be
disabled (enabled) by writing ´1´ (´0´) to the bit shadow_dis. With shadowing disabled, the
content of both MSB and LSB registers is updated by a new value immediately. Unused bits of
the LSB registers may have any value and should be ignored. The (0x02, 0x04, 0x06)
new_data flag of each LSB register is set if the data registers have been updated. The flag is
reset if either the corresponding MSB or LSB part is read.
Two different streams of acceleration data are available, unfiltered and filtered. The unfiltered
data is sampled with 2kHz. The sampling rate of the filtered data depends on the selected filter
bandwidth and is always twice the selected bandwidth (BW = ODR/2). Which kind of data is
stored in the acceleration data registers depends on bit (0x13) data_high_bw. If (0x13)
data_high_bw is ´0´ (´1´), then filtered (unfiltered) data is stored in the registers. Both data
streams are offset-compensated.
The bandwidth of filtered acceleration data is determined by setting the (0x10) bw bit as
followed:
Table 4: Bandwidth configuration
bw
Bandwidth
Update Time
t
ut
00xxx
*)
-
01000
7.81Hz
64ms
01001
15.63Hz
32ms
01010
31.25Hz
16ms
01011
62.5Hz
8ms
01100
125Hz
4ms
01101
250Hz
2ms
01110
500Hz
1ms
01111
unfiltered
0.5ms
1xxxx
*)
-
*) Note: Settings 00xxx result in a bandwidth of 7.81 Hz; settings 1xxxx result in ODR
max
(unfiltered signal). It is recommended to actively set an application specific and an appropriate
bandwidth and to use the range from ´01000b´ to ´01111b´ only in order to be compatible with
future products.