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Data sheet

BMA220

Page 22

BST-BMA220-DS003-08 | Revision 1.15 | August 2011 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.

5.5 Tap-sensing

Tap sensing has the same functionality as a common laptop touch-pad. If 2 taps occur within a

short time, a pre-defined action will be performed by the system. If time between 2 taps is too

long or too short no action happens.

When the serial interface is activated, tap sensing is enabled if any of the tap sensing enable

axis enable bits.

When the preset threshold tt_th is exceeded, a tap-shock is detected. The tap sensing interrupt

is generated only when a second tap is detected within a specified period of time.

The slope between two successive acceleration data has to exceed tt_th to detect a tap-shock.

The time difference between the two successive acceleration values depends on the bandwidth

of the low pass filter. It roughly corresponds to 1/(2*bandwidth).

The time delay tt_dur between two taps is typically between 12,5ms and 500ms. The threshold

is typically between 0.7g and 1.5g in 2g measurement range. Due to different coupling between

sensor and device shell (housing) and different measurement ranges of the sensor these

parameters are configurable.

The criteria for tap sensing are fulfilled and the interrupt is generated if the second tap occurs

after tap_quiet and within tt_dur. The tap sensing direction is determined by the 1

tap. During

tt_quiet period (30ms) no taps should occur. If a tap occurs during tap_quiet period it will be

connoted as new tap.

The slope detection interrupt logic stores the direction of the (first) tap-shock in a status register.

This register will be locked for tap_shock=50ms in order to prevent other slopes to overwrite this

information.

When a tap sensing interrupt is triggered, the signals of the axis that has triggered the interrupt

(tt_first_x, tt_first_y, tt_first_z) and the signal of motion direction (tt_sign) are stored in the

corresponding registers.

The axis on which the biggest slope occurs will trigger the first tap. The second tap will be

triggered by any axis (not necessarily same as the first tap).

The register tap_en defines whether single tap or double tap shall be detected.

In dedicated tap sensing mode, all three axes are enabled for double tap sensing detection.

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