BMA250 Bosch Sensortec, BMA250 Datasheet - Page 26



Manufacturer Part Number
Bosch Sensortec

Specifications of BMA250

Featured Product
BMA250 - Digital, Triaxial Acceleration Sensor
X, Y, Z
Acceleration Range
±2g, 4g, 8g, 16g
256LSB/g, 128LSB/g, 64LSB/g, 16LSB/g
Voltage - Supply
1.62 V ~ 3.6 V
Output Type
I²C™, SPI™
8Hz ~ 1kHz
Mounting Type
Surface Mount
Package / Case
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
For Use With
Other names
Bosch Sensortec
Data sheet
The threshold is set with the value of register (0x28) slope_th. 1 LSB of (0x28) slope_th
corresponds to 1 LSB of acceleration data. Therefore, an increment of (0x28) slope_th is 3.91
mg in 2g-range (7.81 mg in 4g-range, 15.6 mg in 8g-range and 31.3 mg in 16g-range). And the
maximum value is 996 mg in 2g-range (1.99g in 4g-range, 3.98g in 8g-range and 7.97g in 16g-
The time difference between the successive acceleration signals depends on the selected
bandwidth and equates to 1/(2*bandwidth) (Δt=1/(2*bw)). In order to suppress failure signals,
the interrupt is only generated (cleared) if a certain number N of consecutive slope data points is
larger (smaller) than the slope threshold given by (0x28) slope_th. This number is set by the
(0x27) slope_dur bits. It is N = (0x27) slope_dur + 1 for (0x27).
Example: (0x27) slope_dur = 00b, …, 11b = 1decimal, …, 4decimal Enabling (disabling) for each axis
Any-motion detection can be enabled (disabled) for each axis separately by writing ´1´ (´0´) to
bits (0x16) slope_en_x, (0x16) slope_en_y, (0x16) slope_en_z. The criteria for any-motion
detection are fulfilled and the slope interrupt is generated if the slope of any of the enabled axes
exceeds the threshold (0x28) slope_th for [(0x27) slope_dur +1] consecutive times. As soon as
the slopes of all enabled axes fall or stay below this threshold for [(0x27) slope_dur +1]
consecutive times the interrupt is cleared unless interrupt signal is latched. Axis and sign information of any motion interrupt
The interrupt status is stored in bit (0x09) slope_int. The any-motion interrupt supplies additional
information about the detected slope. The axis which triggered the interrupt is given by that one
of bits (0x0B) slope_first_x, (0x0B) slope_first_y, (0x0B) slope_first_z that contains a ´1´. The
sign of the triggering slope is held in bit (0x0B) slope_sign. If (0x0B) slope_sign = ´0´ (´1´), the
sign is positive (negative). Serial interface and dedicated wake-up mode
When serial interface is active, any-motion detection logic is enabled if any of the axis specific
(0x16) slope_en_... register bits are set. To disable the any-motion interrupt, clear all the axis
specific (0x16) slope_en_... bits.
In the dedicated wake-up mode (see chapter 4.2.2), all three axes are enabled for any-motion
detection whether the individual axis enable bits are set or not.
4.8.6 Tap sensing
Tap sensing has a functional similarity with a common laptop touch-pad or clicking keys of a
computer mouse. A tap event is detected if a pre-defined slope of the acceleration of at least
one axis is exceeded. Two different tap events are distinguished: A ‘single tap’ is a single event
within a certain time, followed by a certain quiet time. A ‘double tap’ consists of a first such
event followed by a second event within a defined time frame.
Only one of the tap interrupts can be enabled at the same time. Single tap interrupt is enabled
(disabled) by writing ´1´ (´0´) to bit (0x16) s_tap_en. Double tap interrupt is enabled (disabled)
by writing ´1´ (´0´) to bit (0x16) d_tap_en. If one tries to enable both interrupts by writing ´1´ to
Rev. 1.0
Page 26 / not for publishing
03 March 2011
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as copying and passing on to third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.
Note: Specifications within this document are subject to change without notice.

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