BMC150 datasheet(53/142 Pages) BOSCH

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Datasheet

eCompass BMC150

Page 53

BST-BMC150-DS000-04 | Revision 1.0 | July 2014

Bosch Sensortec

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. Not intended for publication.

4.7.10 High-g interrupt

This interrupt is based on the comparison of acceleration data against a high-g threshold for the

detection of shock or other high-acceleration events.

The high-g interrupt is enabled (disabled) per axis by writing “1” (“0”) to bits (0x17) high_en_x,

(0x17) high_en_y, and (0x17) high_en_z, respectively. The high-g threshold is set through the

(0x26) high_th register. The meaning of an LSB of (0x26) high_th depends on the selected g-

range: it corresponds to 7.81 mg in 2g-range, 15.63 mg in 4g-range, 31.25 mg in 8g-range, and

62.5 mg in 16g-range (i.e. increment depends from g-range setting).

A hysteresis can be selected by setting the (0x24) high_hy bits. Analogously to (0x26) high_th,

the meaning of an LSB of (0x24) high_hy is g-range dependent: it corresponds to an

acceleration difference of 125 mg in 2g-range, 250 mg in 4g-range, 500 mg in 8g-range, and

1000mg in 16g-range (as well, increment depends from g-range setting).

The high-g interrupt is generated if the absolute value of the acceleration of at least one of the

enabled axes (´or´ relation) is higher than the threshold for at least the time defined by the

(0x25) high_dur register. The interrupt is reset if the absolute value of the acceleration of all

enabled axes (´and´ relation) is lower than the threshold minus the hysteresis for at least the

time defined by the (0x25) high_dur register. In bit (0x09) high_int the interrupt status is stored.

The relation between the content of (0x25) high_dur and the actual delay of the interrupt

generation is delay [ms] = [(0x22) low_dur + 1] • 2 ms. Therefore, possible delay times range

from 2 ms to 512 ms. The interrupt will be cleared immediately once acceleration is lower than

threshold.

4.7.10.1 Axis and sign information of high-g interrupt

The axis which triggered the interrupt is indicated by bits (0x0C) high_first_x, (0x0C)

high_first_y, and (0x0C) high_first_z. The bit corresponding to the triggering axis contains a “1”

while the other bits hold a “0”. These bits are cleared together with clearing the interrupt status.

The sign of the triggering acceleration is stored in bit (0x0C) high_sign. If (0x0C) high_sign = “0”

(“1”), the sign is positive (negative).

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