The expansion board contains three buttons. Two of the three buttons have predefined operation, while the third button is user defined. The three buttons are titled:
Power Button (PWR BTN)
DNX Boot Button (DNX BOOT)
General Purpose Button (GP BTN)
The power button is connected to the PMIC_PWRBTN_N signal of the module. When the button is pressed, the PMIC_PWRBTN_N signal is pulled to ground, driving the PMIC_PWRBTN_N signal to a low state. When the button is released, the PMIC_PWRBTN_N signal is pulled high, to +VSYS in the module.
The low time durations of the PMIC_PWRBTN_N signal result in various actions on the module. Refer to Power Delivery, Signaling, and Reset
for specific information and usage for the PMIC_PWRBTN_N signal and the resulting actions.
The DNX boot button is connected to the UART_2_TXD signal of the module. When the button is pressed, the UART_2_TXD signal is pulled high through a 100Ω resistor to +VDD1 (1.8 volts). When the button is released, the UART_2_TXD signal is left floating, but relies on a 20kΩ internal pull-down within the module SoC to insure a low-level signal.
The DNX boot button is used to initiate a BIOS programming cycle when pressed and held during a power-up cycle. At the rising edge of the module’s PMIC_PWRGOOD signal (for example during a power-up cycle), the UART_2_TXD is sampled by the module SoC. If the UART_2_TXD is sampled as a high signal, then the SoC initiates a BIOS update from the USB Type-C port. Similarly, if the UART_2_TXD signal is sampled as a low signal (for example DNX boot button released) on the rising edge of PMIC_PWRGOOD, then a BIOS update is not initiated and the boot process continues normally.
General Purpose Button (SW1)
The general purpose button is available to be defined by the software developer. It is connected to the BTN_N signal of the module. When the button is pressed, the BTN_N signal is shorted to ground, driving the BTN_N signal to a low state. When the button is released, the BTN_N signal is pulled high, to +VDD1 (1.8 volts).
Jumper block J14 provides the ability to selectively enable boot sources for the expansion board, specifically, the ability to enable booting from the SD card or from eMMC.
The location of the jumper block is shown in the figure below.
The jumper must be installed prior to a power-up of the expansion board, as the state of the jumpers is sampled by the module at the rising edge of the PMIC_PWRGOOD signal, during the power-up process.
Placing a jumper across pins 1 and 2 of J14 enables booting from eMMC.
Placing a jumper across pins 3 and 4 of J14 enables booting from the SD card.
The default configuration is no jumpers installed.
A main power LED is located near the power switch (SW2) and is enabled when all expansion board power rails are stabilized and a general power good state is achieved.
There are four general purpose LEDs located in the upper center area of the expansion board. See the figure below for the location of the LEDs. The LED is turned on when the related GPIO signal is high, regardless of whether the GPIO is configured as an input or an output.
In addition to being user programmable, these LEDs are used by the BIOS to indicate progression of the boot process or other information. All four LEDs are illuminated when BIOS passes code execution to the operating system (OS). Depending on the BIOS build, these GPIO lines can be left high or low, and set as either input or output. See the BIOS release notes for additional information
General Purpose LED Mapping
LED Reference Designator
Breakout Pin #