Specifications

BMA180
Preliminary data sheet
Bosch Sensortec
Rev. 1.0 Page 22 / - proprietary information - 06 March 2009
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Specifications within this document are preliminary and subject to change without notice. Document is not intended for publication.
time
|a|
Freefall threshold
Evaluation duration
INT
low
high
Latched INT
High-g threshold
acceleration
Hysteresis
Reset INT
6 Internal logic functions
The sensor IC can inform the host system about specific conditions (e.g. new data ready flag or
acceleration thresholds passed) by setting an interrupt pin high even if interface communication
is not taking place. This feature can be used as “free-fall or low-g indicator”, “wake-up” or “data
ready flag” for instance.
The interrupt performance can be programmed by means of control bits. Thus the criteria to
identify a special event can be tailored to a customer’s application and the sensor IC output can
be defined specifically.
6.1 Free-fall logic (or low-g interrupt logic)
For free-fall detection the absolute value of the acceleration data of all axes are investigated
(global criteria). A free-fall situation is likely to occur when all axes fall below the low threshold
value. The interrupt pin will be raised high if the threshold is passed for a minimum duration.
The duration time can be programmed.
Figure 5: Schematic behaviour in case of low-g detection (e. g. for free-fall)
The function “Free-fall Interrupt” can be switched on/off by a control bit which is located within
the image of the non-volatile memory. Thus this functionality can be stored as default setting of
the sensor IC (EEPROM) but can also rapidly be changed within the image.
The reset of the free-fall interrupt can be accomplished by means of a master reset of the
interrupt flag (latched interrupt) or the reset can be triggered by the acceleration signal itself
(validation of a programmable “hysteresis”).
Further details concerning free-fall and other interrupts, see 7.9