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32142D–06/2013
ATUC64/128/256L3/4U
(MBLEN) when using the QMatrix acquisition method. Two additional handshakes support DMA-
Touch by regulating transfers from memory to the DMATouch State Write Register (DMATSW)
and from the DMATouch State Read Register (DMATSR) to memory. The Peripheral DMA Con-
troller must be configured properly and enabled in order to perform direct memory access
transfers to/from the CAT module.
31.5.6
Analog Comparators
When the CAT module is performing QMatrix acquisition, it requires that on-chip analog compar-
ators be used as part of the process. These analog comparators are not controlled directly by
the CAT module, but by a separate Analog Comparator (AC) Interface. This interface must be
configured properly and enabled before the CAT module is used. This includes configuring the
generic clock input for the analog comparators to the proper sampling frequency.
The CAT will automatically use the negative peripheral events from the AC Interface on every Y
pin in QMatrix mode. When QMatrix acquisition is used the analog comparator corresponding to
the selected Y pins must be enabled and converting continuously, using the Y pin as the positive
reference and the ACREFN as negative reference.
31.5.7
Debug Operation
When an external debugger forces the CPU into debug mode, the CAT continues normal opera-
tion. If the CAT is configured in a way that requires it to be periodically serviced by the CPU
through interrupts or similar, improper operation or data loss may result during debugging.
31.6
Functional Description
31.6.1
Acquisition Types
The CAT module can perform several types of QTouch acquisition from capacitive touch sen-
sors: autonomous QTouch (one sensor only), DMATouch, QTouch group A, and QTouch group
B. The CAT module can also perform QMatrix acquisition. Each type of acquisition has an asso-
ciated set of pin selection and configuration registers that allow a large degree of flexibility.
The following schematic diagrams show typical hardware connections for QTouch and QMatrix
sensors, respectively:
Figure 31-2. CAT Touch Connections
AVR32 Chip
QTouch
Sensor
Cs (Sense Capacitor)
SNSKn
SNSn