BMA150 datasheet(51/55 Pages) ETC2

51 / 55 page

Data sheet

BMA150

Triaxial, digital acceleration sensor

Bosch Sensortec

Rev. 1.5

Page 51

30 May 2008

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.

9. 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 “freefall 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.

9.1 Freefall logic

For freefall detection the absolute value of the acceleration data of all axes are investigated

(global criteria). A freefall situation is likely to occur when all axes fall below a lower threshold

value (“LG_thres”). The interrupt pin will be raised high if the threshold is passed for a minimum

duration. The duration time can be programmed in units of ms (max. 255ms).

The function “Freefall 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 freefall 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”).

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