AN3308 datasheet(31/52 Pages) STMICROELECTRONICS

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AN3308

Click and double click recognition

Doc ID 18198 Rev 1

31/52

8.2

Double click

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

after a first click, a second click is recognized. The recognition of the second click occurs

only if the event satisfies the rules defined by the latency and windows registers.

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

is delayed for an interval defined by the latency register. This means that after the first click

has been recognized, the second click detection procedure starts only if the input

acceleration exceeds the threshold after the latency window but before the window has

expired (Figure 15 (a)), or if the acceleration is still above the threshold after the latency has

expired (Figure 16 (b)).

Once the second click detection procedure is initiated, the second click is recognized with

the same rule as the first: the acceleration must return below the threshold before the

TimeLimit has expired.

It is important to appropriately define the latency window to avoid unwanted clicks due to

spurious bouncing of the input signal.

Figure 15.

Single and double click recognition

Figure 15 illustrates a single click event (a) and a double click event (b). The device is able

to distinguish between (a) and (b) by changing the settings of the TAP_CFG register from

single to double click recognition.

(a)

(b)

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