19

AT42QT1060 [DATASHEET]

9505H–AT42–04/2015

5.9

Address 14: Drift Option

DRIFT: there are two types of drift option: normal and relative referencing.

If DRIFT = 0, relative referencing and normal drift are enabled.

If DRIFT = 1, only normal drift is enabled.

Relative referencing compensates for fast signal drifts that are common to all keys. This mode is suitable if the keys

are placed close to each other and have closely matched burst lengths (see Section 2.12.3 on page 9). Normal

drifting is also carried out but at a slower rate compared to the relative referencing drift rate.

Default: 1 (relative referencing Off)

5.10

Address 15: Positive Recalibration Delay

POSITIVE RECALIBRATION DELAY: If any key is found to have a significant drop in capacitance, that is, an “away

from touch” signal, then this is deemed to be an error condition. If this condition persists for more than the Positive

Recalibration Delay (PRD) period, then an automatic recalibration is carried out on all keys.

The condition that the error is triggered on depends on the drift compensation mode. If relative referencing drifting is

enabled (DRIFT = 0), then an “away from touch” delta of more than four counts triggers the error. If only normal

mode drifting is enabled (DRIFT = 1), then an “away from touch” delta of more than 75% of the NTHR triggers the

error.

In LP mode the Positive Recalibration Delay is the PRD value multiplied by 16 ms cycle time; in Free Run Mode the

Positive Recalibration delay is the PRD value multiplied by the minimum cycle time (~7 ms, but depends on Cs and

design).

Default: 40 (40 × 16 ms = 640 ms; default LP is 32 ms)

5.11

Address 16 – 21: NTHR Keys 0 – 5

NTHR Keys 0 – 5: these 8-bit values set the threshold value for each key to register a detection.

Default: 10 counts

Table 5-9.

Drift Option

Address

b7

b6

b5

b4

b3

b2

b1

b0

14

Reserved

DRIFT

Table 5-10. Positive Recalibration Delay

Address

b7

b6

b5

b4

b3

b2

b1

b0

15

POSITIVE RECALIBRATION DELAY

Table 5-11.

NTHR Keys 0 – 5

Address

b7

b6

b5

b4

b3

b2

b1

b0

16–21

MSB

LSB