AN3393 datasheet(83/103 Pages) STMICROELECTRONICS

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AN3393

Examples of state machine configurations

103

Figure 23. Double-turn output

9.5

Double-tap

The implementation is intended to recognize the double-tap on the device.

The first two states (GNTH1 | TI1) are used to create a “pre-silence” time window, the NEXT

condition is the Timer1. If one or more axes become greater than threshold 1, the RESET

condition is satisfied and the program pointer is reset. After that there is the real first tap

detection composed of two states, the first one is composed of (NOP | GNTH2), where the

next condition is satisfied when one or more triggered axes exceed threshold 2. In the

second state (TI3 | LNTH2), it is checked whether the acceleration value on the axis

becomes lower than threshold 2 within a time defined by Timer 3. The result of these states

is to create a time window (TI3) where the acceleration is first higher, and then lower, than

threshold 2.

When the first tap has been detected, the system waits 20 ms (TI4), again doing a pre-

silence time window (GNTH1 | TI1) and starting with the second tap detection.

AM14788V1

Table 92. Register configuration for double-tap application

Address

Value

CTRL_REG1

21h

01h

CTRL_REG3

23h

48h

CTRL_REG4

20h

67h

CTRL_REG5

24h

00h

TIM4_1

50h

02h

TIM3_1

51h

01h

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