ATUC128L3U_14 Datasheet, PDF (777/963 Pages) ATMEL Corporation – High-performance, Low-power 32-bit Atmel

ATUC64/128/256L3/4U
31.6.3
The Y and YK pins remain clamped to ground apart from the specified number of burst pulses,
when charge is transferred and captured into the sampling capacitor.
Capacitive Count Acquisition
For the QMatrix, QTouch group A, and QTouch group B types of acquisition, the module
acquires count values from the sensors, buffers them, and makes them available for reading in
the ACOUNT register. Further processing of the count values must be performed by the CPU.
When the module performs QMatrix acquisition using multiple Y lines, it starts the capture for
each Y line at the appropriate time in the burst sequence so that all captures finish simultane-
ously. For example, suppose that an acquisition is performed on Y0 and Y1 with BURST0=53
and BURST1=60. The module will first toggle the X line 7 times while capturing on Y1 while Y0
and YK0 are clamped to ground. The module will then toggle the X line 53 times while capturing
on both Y1 and Y0.
31.6.4
Autonomous QTouch and DMATouch
For autonomous QTouch and DMATouch, a complete detection algorithm is implemented within
the CAT module. The additional parameters needed to control the detection algorithm must be
specified by the user in the ATCFG2 and ATCFG3 registers.
Autonomous QTouch and DMATouch sensitivity and out-of-touch sensitivity can be adjusted
with the SENSE and OUTSENS fields, respectively, in ATCFG2. Each field accepts values from
one to 255 where 255 is the least sensitive setting. The value in the OUTSENS field should be
smaller than the value in the SENSE field.
To avoid false positives a detect integration filtering technique can be used. The number of suc-
cessive detects required is specified in the FILTER field of the ATCFG2 register.
To compensate for changes in capacitance the CAT can recalibrate the autonomous QTouch
sensor periodically. The timing of this calibration is done with the NDRIFT and PDRIFT fields in
the Configuration register, ATCFG3. It is recommended that the PDRIFT value is smaller than
the NDRIFT value.
The autonomous QTouch sensor and DMATouch sensors will also recalibrate if the count value
goes too far positive beyond a threshold. This positive recalibration threshold is specified by the
PTHR field in the ATCFG3 register.
The following block diagram shows the sequence of acquisition and processing operations used
by the CAT module. The AISR written bit is internal and not visible in the user interface.
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