Figure 285. Surface Charge Transfer Analog I/O Group Structure - STMicroelectronics STM32F05 series Reference Manual

RM0091
The remaining GPIOs are dedicated to the electrodes and are commonly called channels.
For some specific needs (such as proximity detection), it is be possible to simultaneously
enable more than one channel per analog I/O group.

Figure 285. Surface charge transfer analog I/O group structure

Note: Gx_IOy where x is the analog I/O group number and y the GPIO number within the selected
group.
The surface charge transfer acquisition principle consists of charging an electrode
capacitance (C
capacitor (C
threshold (V
is a direct representation of the size of the electrode capacitance.
The Table 95
channel 1. States 3 to 7 are repeated until the voltage across C
threshold. The same sequence applies to the acquisition of the other channels. The
electrode serial resistor R
Electrode 1
R
S1
C
X1
C
S
Electrode 2
R
S2
C
X2
Electrode 3
R
S3
C
X3
) and transferring a part of the accumulated charge into a sampling
X
). This sequence is repeated until the voltage across C
S
in our case). The number of charge transfers required to reach the threshold
IH
details the charge transfer acquisition sequence of the capacitive sensing
improves the ESD immunity of the solution.
S
Doc ID 018940 Rev 1
G1_IO1
G1_IO2
G1_IO3
G1_IO4
Touch sensing controller (TSC)
Analog
I/O group
reaches a given
S
reaches the given
S
683/742