AT42QT1111-MU Datasheet, PDF (36/50 Pages) ATMEL Corporation – QTouch 11-key Sensor IC

Table 7-16. Negative Threshold/Negative Hysteresis (Continued)
Address
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
25
KEY_6_NTHR
26
KEY_7_NTHR
27
KEY_8_NTHR
28
KEY_9_NTHR
29
KEY_10_NTHR
Bit 1
Bit 0
KEY_6_NHSYT
KEY_7_NHSYT
KEY_8_NHSYT
KEY_9_NHSYT
KEY_10_NHSYT
KEY_n_NTHR: the negative threshold for key n (where n is 0–10).
The negative threshold determines how much the signal must fall (compared to the reference)
before a key is considered to be “In Detect”. This level will generally need to be tuned
individually for each key. To disable an individual key, set the threshold for that key to 0.
KEY_n_NHYST: the negative hysteresis applied to key n detection threshold (where n is
0 – 10).
Negative Hysteresis operates as a “modifier” for the negative threshold in order to provide a
greater degree of control over the detection of a “Touch”. When a key signal is first detected as
being under the negative threshold, the threshold is reduced by a factor corresponding to the
selected negative hysteresis. This means that the key will not go in and out of detection when
the signal is on the borderline between drift-compensation or touch detection.
The settings for negative hysteresis are:
00 No change to negative threshold
01 12.5% reduction in negative threshold
10 25% reduction in negative threshold
11 37.5% reduction in negative threshold
Default KEY_n_NTHR value:
Default KEY_n_NHYST value:
10 counts
2 (25 percent)
36 AT42QT1111-MU/AT42QT1111-AU
9571A–AT42–02/10