ORCA SBC/Interfaces and Connectors/Touchscreen
|1.0.0||Dec 2021||First release|
Touchscreen interface[edit | edit source]
Description[edit | edit source]
The Evaluation Kit default LCD panel (provided on request) interfaces the touchscreen via USB, thus it is connected to J3 or J4, see USB ports section.
Many touchscreen types use instead an I2C interface with two additional control signals (RST, IRQ).
To use these type of touchscreens the interface signals can be routed to the expansion connector J8.
An external circuit is recommended to correctly conditioning the interface signals, such as buffers and pull up/down, according to the touchscreen specifications.
Signals[edit | edit source]
The following table describes the available I2C signals on J8 connector, see GPIO section for available control signals:
|Pin#||SOM Pin#||Pin name||Pin function||Pin Notes|
|1, 17||-||3V3_CB||+3.3V||BOARD_PGOOD driven rail|
|2, 4||-||5V_VIN||+5V||Always powered|
|6, 9, 14, 20, 25, 30, 34, 39||-||DGND||Ground|
All the I2C signals use 0 - 3.3V levels, external pull-ups to
3V3_CB are needed.
Device mapping[edit | edit source]
The device is typically mapped to
/dev/touchscreen0 device in Linux.
The touch controller is attached to the generic Linux input event interface (evdev).
For I2C touchscreen controllers a dedicated node in the device-tree has to be configured to correctly bind the driver.
Device usage[edit | edit source]
The touchscreen device is often passed as parameter to the user interface application or is automatically discovered.
Touchscreen can be tested with the
evtest tool that prints the finger coordinates to the console.