Touch-Sensing Button; Table 18. Touch-Sensing-Related Configuration Elements - ST STM32L4R9I User Manual

Hardware layout and configuration
6.26

Touch-sensing button

The STM32L4R9I-EVAL main board supports a touch-sensing button based on either RC
charging or the charge-transfer technique. The latter is enabled, by default.
The touch-sensing button is connected to the PC6 port of STM32L4R9AII6 and the related
charge capacitor is connected to PC7.
An active shield is designed in layer 2 of the main PCB, under the button footprint. It allows
the reduction of disturbances from other circuits to prevent false touch detections.
The active shield is connected to the PB6 port of STM32L4R9AII6 through the resistor R22.
The related charge capacitor is connected to PB7.
Table 18
them serve to enable or disable its operation. However, most of them serve to optimize the
touch-sensing performance, by isolating copper tracks to avoid disturbances due to their
antenna effect.
.
Element
R44
SB21
R46
SB19
SB20
R26
SB14
SB15
42/77
shows the configuration elements related to the touch-sensing function. Some of

Table 18. Touch-sensing-related configuration elements

Setting
PC6 port is routed to the CN6 connector of the daughterboard.
ON
This setting is not good for the robustness of touch sensing.
OFF Default setting: PC6 port is cut from CN6.
OFF Default setting: PC6 is not routed to motor control.
PC6 is routed to motor control.
ON
This setting is not good for the robustness of touch sensing.
PC7 port is routed to the CN6 connector of the daughterboard.
ON
This setting is not good for the robustness of touch sensing.
OFF Default setting: PC7 port is cut from CN6.
OFF Default setting: PC7 is not routed to motor control.
PC7 is routed to motor control.
ON
This setting is not good for the robustness of touch sensing.
PC7 is not routed to the sampling capacitor. Touch sensing cannot
OFF
operate.
Default setting: PC7 is routed to the sampling capacitor. Touch
ON
sensing is available.
PB6 port is routed to the CN5 connector of the daughterboard.
ON
This setting is not good for the robustness of touch sensing.
OFF Default setting: PB6 port is cut from CN5.
OFF Default setting: PB6 is not routed to motor control.
PB6 is routed to motor control.
ON
This setting is not good for the robustness of touch sensing.
PB6 is not routed to the active shield under the touch-sensing button.
OFF
This setting is not good for the robustness of touch sensing.
Configuration
UM2248 Rev 5
UM2248