ORCA SOM/ORCA Evaluation Kit/Interfaces and Connectors/Touchscreen

History
Issue Date	Notes
2021/12/10	First release

Touchscreen interface

Description

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.

Touchscreen connector

Signals

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
19		ECSPI2_MOSI	I2C3_SDA
21		ECSPI2_MISO	I2C4_SCL
22		SAI5_MCLK	I2C5_SDA
23		ECSPI2_SCLK	I2C3_SCL
24		ECSPI2_SS0	I2C4_SDA
32		SAI5_RXFS	I2C6_SCL
38		SAI5_RXD0	I2C5_SCL
40		SAI5_RXC	I2C6_SDA
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

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

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.

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