STM8T143 datasheet(16/65 Pages) STMICROELECTRONICS

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STM8T143 processing

STM8T143

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5.3

Detection and release thresholds

During the detection operation, after calibration is over, the STM8T143 switches between

three operating states: no detection, proximity detection, and touch detection. The switch

between these states is driven by the difference between the signal and the reference.

The system goes from no detection to proximity detection state when the (reference - signal)

is higher than the proximity threshold (PTh). In this state, the ECS is halted and the

reference is frozen.

The system goes from no detection or proximity detection state to touch detection state

when the (reference - signal) is higher than the touch threshold (TTh). When this happens,

the reference value is changed to reflect the touch state after the delay tDYCAL. This process

is called dynamic calibration (DYCAL).

The system goes from the touch detection to no detection state when the (signal -

reference) goes above the release threshold (RTh). At this point, another DYCAL occurs for

the reference to represent the untouched state again.

For higher flexibility, several proximity and touch detection thresholds are available and

independently selectable through option byte: one PTh and one TTh.

•

The touch thresholds allow the touch sensitivity to be adapted to the panel thickness

and the electrode sensitivity.

•

The proximity thresholds allow the STM8T143 device to adapt to various surroundings

and to tune the detection distance.

The release threshold is a ratio of the touch threshold noted (TTh). TTh is selected by the

“touch detection threshold” option bits. The ratio is selected by the “release threshold ratio”

option bits.

A time filtering, similar to the debouncing of the mechanical switches, is applied to avoid

noise induced detections.

Please refer to Section 5.6: Debounce filter for operation details.

Figure 8 simplifies the proximity and touch detection event according to the signal variation

“

Δ (signal)”. The Δ (signal) is the absolute value of the reference minus the signal.

STM8T143 Datasheet(PDF) 16 Page - STMicroelectronics