RM0367 Rev 7 421/1043
RM0367 Touch sensing controller (TSC)
432
18.3.8 Acquisition mode
The touch sensing controller offers two acquisition modes:
• Normal acquisition mode: the acquisition starts as soon as the START bit in the
TSC_CR register is set.
• Synchronized acquisition mode: the acquisition is enabled by setting the START bit in
the TSC_CR register but only starts upon the detection of a falling edge or a rising
edge and high level on the SYNC input pin. This mode is useful for synchronizing the
capacitive sensing channels acquisition with an external signal without additional CPU
load.
The GxE bits in the TSC_IOGCSR registers specify which analog I/O groups are enabled
(corresponding counter is counting). The C
S
voltage of a disabled analog I/O group is not
monitored and this group does not participate in the triggering of the end of acquisition flag.
However, if the disabled analog I/O group contains some channels, they are pulsed.
When the C
S
voltage of an enabled analog I/O group reaches the given threshold, the
corresponding GxS bit of the TSC_IOGCSR register is set. When the acquisition of all
enabled analog I/O groups is complete (all GxS bits of all enabled analog I/O groups are
set), the EOAF flag in the TSC_ISR register is set. An interrupt request is generated if the
EOAIE bit in the TSC_IER register is set.
In the case that a max count error is detected, the ongoing acquisition is stopped and both
the EOAF and MCEF flags in the TSC_ISR register are set. Interrupt requests can be
generated for both events if the corresponding bits (EOAIE and MCEIE bits of the TSCIER
register) are set. Note that when the max count error is detected the remaining GxS bits in
the enabled analog I/O groups are not set.
To clear the interrupt flags, the corresponding EOAIC and MCEIC bits in the TSC_ICR
register must be set.
The analog I/O group counters are cleared when a new acquisition is started. They are
updated with the number of charge transfer cycles generated on the corresponding
channel(s) upon the completion of the acquisition.
For code example, refer to A.10.1: TSC configuration code example.
18.3.9 I/O hysteresis and analog switch control
In order to offer a higher flexibility, the touch sensing controller also allows to take the control
of the Schmitt trigger hysteresis and analog switch of each Gx_IOy. This control is available
whatever the I/O control mode is (controlled by standard GPIO registers or other
peripherals) assuming that the touch sensing controller is enabled. This may be useful to
perform a different acquisition sequence or for other purposes.
In order to improve the system immunity, the Schmitt trigger hysteresis of the GPIOs
controlled by the TSC must be disabled by resetting the corresponding Gx_IOy bit in the
TSC_IOHCR register.
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