BMA255 datasheet(31/119 Pages) BOSCH

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BMA255

Data sheet

Page 31

BST-BMA255-DS004-05 | Revision 1.2 | August 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.

4.7.6 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.

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.

While temporary latching is used do not simultaneously enable single tap interrupt and double

tap interrupt.

The status of the single tap interrupt is stored in bit (0x09) s_tap_int, the status of the double

tap interrupt is stored in bit (0x09) d_tap_int.

The slope threshold for detecting a tap event is set by bits (0x2B) tap_th. The meaning of

(0x2B) tap_th depends on the range setting. 1 LSB of (0x2B) tap_th corresponds to a slope of

62.5mg in 2g-range, 125mg in 4g-range, 250mg in 8g-range, and 500mg in 16g-range.

In figure 8 the meaning of the different timing parameters is visualized:

tap_shock

tap_quiet

tap_dur

tap_shock

tap_quiet

time

12.5 ms

single tap detection

double tap detection

slope

time

12.5 ms

time

1st tap

2nd tap

tap_th

Figure 8: Timing of tap detection

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