ST STM32L4+ Series Reference Manual page 1051

RM0432
31.3.7 Sampling capacitor I/O and channel I/O mode selection
To allow the GPIOs to be controlled by the touch sensing controller, the corresponding
alternate function must be enabled through the standard GPIO registers and the GPIOxAFR
registers.
The GPIOs modes controlled by the TSC are defined using the TSC_IOSCR and
TSC_IOCCR register.
When there is no ongoing acquisition, all the I/Os controlled by the touch sensing controller
are in default state. While an acquisition is ongoing, only unused I/Os (neither defined as
sampling capacitor I/O nor as channel I/O) are in default state. The IODEF bit in the
TSC_CR register defines the configuration of the I/Os which are in default state. The table
below summarizes the configuration of the I/O depending on its mode.
IODEF bit
(output push-pull low)
(output push-pull low)
(input floating)
(input floating)
Unused I/O mode
An unused I/O corresponds to a GPIO controlled by the TSC peripheral but not defined as
an electrode I/O nor as a sampling capacitor I/O.
Sampling capacitor I/O mode
To allow the control of the sampling capacitor I/O by the TSC peripheral, the corresponding
GPIO must be first set to alternate output open drain mode and then the corresponding
Gx_IOy bit in the TSC_IOSCR register must be set.
Only one sampling capacitor per analog I/O group must be enabled at a time.
Channel I/O mode
To allow the control of the channel I/O by the TSC peripheral, the corresponding GPIO must
be first set to alternate output push-pull mode and the corresponding Gx_IOy bit in the
TSC_IOCCR register must be set.
For proximity detection where a higher equivalent electrode surface is required or to speed-
up the acquisition process, it is possible to enable and simultaneously acquire several
channels belonging to the same analog I/O group.
Note: During the acquisition phase and even if the TSC peripheral alternate function is not
enabled, as soon as the TSC_IOSCR or TSC_IOCCR bit is set, the corresponding GPIO
analog switch is automatically controlled by the touch sensing controller.
Table 213. I/O state depending on its mode and IODEF bit value
Acquisition
status
0
No
0
Ongoing
1
No
1
Ongoing
Unused I/O
mode
Output push-pull
low
Output push-pull
low
Input floating
Input floating
RM0432 Rev 6
Touch sensing controller (TSC)
Channel I/O
capacitor I/O
mode
Output push-pull Output push-pull
low
-
Input floating Input floating
-
Sampling
mode
low
-
-
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