AT42QT1111-MU Datasheet, PDF (31/50 Pages) ATMEL Corporation – QTouch 11-key Sensor IC

AT42QT1111-MU/AT42QT1111-AU
Where data is being sent by the host, a 1-byte CRC should be sent. The QT1111 returns the
expected CRC byte in the same transaction the CRC byte is sent. In this way, the host can
immediately determine whether the setup data bytes were received correctly.
Default GUARD_KEY value:
Default GD_EN value:
Default CHG value:
Default CRC value:
0 (Key 0)
0 (disabled)
0 (data mode)
0 (disabled)
7.6 Address 2: Detect Integrator Limit (DIL)/Drift Hold Time (DHT)
Table 7-5. Detect Integrator/Drift Hold Time
Address
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
2
DIL
DHT
DIL: the detection integrator (DI) limit. To suppress false detections caused by spurious events
like electrical noise, the device incorporates a DI counter mechanism. A per-key counter is
incremented each time the channel has exceeded its threshold and stayed there for a number of
acquisitions in succession, without going below the threshold level. When this counter reaches a
preset limit the channel is finally declared to be touched. If on any acquisition the delta is not
seen to exceed the threshold level, the counter is cleared and the process has to start from the
beginning.
Note: A setting of 0 for DI is invalid; the valid range is 1 to 15.
DHT: the drift hold time. After a key-touch has been removed, the QT1111 pauses in the
implementation of its “Drift” compensation for a time. After this time has expired, drift
compensation continues as normal. The “Drift Hold Time” is a multiple of 160 ms, providing
options from 0 to 2400 ms.
Default DIL value:
Default DHT value:
3
8 (1280 ms)
7.7 Address 3: Positive Threshold (PTHR)/Positive Hysteresis (PHYST)
Table 7-6.
Address
3
Positive Threshold (THR)/Positive Hystereis (HYST)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
PTHR
Bit 1
Bit 0
PHYST
PTHR: the positive threshold for the signal. If a key signal is significantly higher than the
reference signal, this typically indicates that the calibration data is no longer valid. In other
words, some factor has changed since the calibration was carried out, thus rendering it invalid.
Generally this is compensated for by the drift, but the greater the difference the longer this will
take. In order to speed up this correction, the positive threshold is used: if the positive threshold
is exceeded, the QT1111 (that is, all keys) is recalibrated.
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