BMA253
Data sheet
Page 18
4.3 Sensor data
4.3.1 Acceleration data
The width of acceleration data is 12 bits given in two´s complement representation. The 12 bits
for each axis are split into an MSB upper part (one byte containing bits 11 to 4) and an LSB
lower part (one byte containing bits 3 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
Update Time
bw
Bandwidth
tut
00xxx
01000
01001
01010
01011
01100
01101
01110
01111
1xxxx
*)
-
7.81Hz
15.63Hz
31.25Hz
62.5Hz
125Hz
250Hz
500Hz
1000Hz
*)
64ms
32ms
16ms
8ms
4ms
2ms
1ms
0.5ms
-
*) Note: Settings 00xxx result in a bandwidth of 7.81 Hz; settings 1xxxx result in a bandwidth of
1000 Hz. 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.
BST-BMA253-DS000-01 | Revision 1.0 | August 2015
Bosch Sensortec
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Note: Specifications within this document are subject to change without notice.
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