STM8T141 datasheet(15/50 Pages) STMICROELECTRONICS

15 / 50 page

STM8T141

STM8T processing

Doc ID 15699 Rev 7

15/50

5.3.2

Reference freeze timeout

To prevent an object under detection from influencing the reference value, the ECF is halted

as soon as a detection happens. Consequently, the reference is frozen.

In order to be able to recover from a sudden environment change, the reference freeze ends

after a maximum programmable delay called the “reference freeze timeout” (tRFT).

When a detection lasts longer than the tRFT, the ECF is enabled again and the reference

moves toward the detection signal. After a short period of time, the difference between the

signal and the reference become smaller than the detection threshold and the device

reports no detection.

Note:

Reference freeze timeout was incorrectly called “recalibration timeout” in previous versions

of this document.

Figure 9.

Reference freeze timeout

See max values of tRFT in Table 16: General capacitive sensing characteristics.

Between the moment when the finger is removed from the sensor and the instant the reference - DTh curve

crosses the signal limit, the device is unable to detect a new touch. This delay is called “masked detection

window”. It depends on the environmental change or object signal variation speed inside the electrode’s

field. The detection threshold also impacts the masked detection window.

STM8T141 数据表(PDF) 15 Page - STMicroelectronics