How to check and set LDO3OUT for a second PHY?

How do I check what LDO3OUT is set to, what does it need to be, and how do I set it, in order for the 2nd ethernet port on the IMX8X to be brought up?

According to the Apalis IMX8X datasheet: The secondary RGMII/RMII Ethernet interface needs special attention regarding the supply voltage level. The RGMII/RMII voltage is switchable through LDO3OUT of the PMIC PF8100. The voltage level must be defined by software configuration. During the power-up sequence, the IO voltage is set to 3.3V by default. All the RGMII/RMII signals are configured as GPIO inputs with enabled pulldown resistors. If the interface is used with 1.8V IO voltage, it is important to configure first the LDO3OUT voltage and then change the alternate function to RGMII/RMII. This ensures full compatibility with 1.8V RGMII signal levels.

If the secondary Ethernet interface is used as RGMII, the output voltages are limited to 1.8V and 2.5V. For RMII and other alternate functions (e.g., GPIO) of these pins, also 3.3V logic level is suitable. Please note that the ENET1_MDC and ENET1_MDIO are always set to 3.3V, independent of the RGMII/RMII signals’ output voltage settings.


Yes the MDIO interface is on a different port and this one stays at 3.3 volt.
If you sent an email to support (at) We can sent you a sample schematic for the second PHY.

Best Regards,

Matthias Gohlke