Q: What PHY features can be bootstrapped at power up?
A: The PHYs hardware configuration pins allow users to predefine the personality of the PHY for unmanaged applications. The features that can be configured by bootstrapping are as follows:
- PHY Address
- Forced/Advertised mode
- PHY Speed
- Software Powerdown Mode after Reset
- Downspeed Enable
- Energy Detect Powerdown Mode
- EEE Enable
- MAC Interface Selection (RGMII/RMII/MII)
Unmanaged configurations allow the PHY to power up in a particular condition without the need to communicate with the part over the MDIO interface. This means that a link can be brought up quite quickly after power on if there is a link partner present.
The hardware pin configurations are set using external resistors on various pins. Review the datasheet section on Hardware configuration pins for full details.
Note that some pins use 4-level strapping (Mode 1-4), whereas other pins only use two level strapping (high & low).
The PHY address pins use two level strapping.