AN4650 datasheet(44/102 Pages) STMICROELECTRONICS

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Interrupt generation

AN4650

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DocID027415 Rev 1

4.5.1

Single tap

If the device is configured for single-tap event detection, an interrupt is generated when the

slope data on the selected channel exceed the programmed threshold, and return below it

within the Shock time window.

In the single-tap case, if the LIR bit of the TAP_CFG register is set to 0, the interrupt is kept

high for the duration of the Quiet window.

In order to enable the latch feature on the single-tap interrupt signal, both the LIR bit and the

INT1_DOUBLE_TAP (or INT2_DOUBLE_TAP) bit of MD1_CFG (MD2_CFG) have to be set

to 1: the interrupt is kept high until the TAP_SRC register is read.

The SINGLE_DOUBLE_TAP bit of WAKE_UP_THS has to be set to 0 in order to enable

single-tap recognition only.

In case (a) of Figure 14 the single-tap event has been recognized, while in case (b) the tap

has not been recognized because the slope data fall under the threshold after the Shock

time window has expired.

Figure 14. Single-tap event recognition

4.5.2

Double tap

If the device is configured for double-tap event detection, an interrupt is generated when,

after a first tap, a second tap is recognized. The recognition of the second tap occurs only if

the event satisfies the rules defined by the Shock, the Latency and the Duration time

windows.

In particular, after the first tap has been recognized, the second tap detection procedure is

delayed for an interval defined by the Quiet time. This means that after the first tap has been

recognized, the second tap detection procedure starts only if the slope data exceed the

threshold after the Quiet window but before the Duration window has expired. In case (a) of

Figure 15, a double-tap event has been correctly recognized, while in case (b) the interrupt

has not been generated because the slope data exceed the threshold after the window

interval has expired.

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