Configuration
UM0896
10/43
Doc ID 17009 Rev 1
5 Configuration
5.1 Ethernet
An Ethernet PHY U5 is available on the board. It is connected through the media
independent interfaces (MII, and reduced MII, RMII) to the Ethernet MACs of the STM32™
microcontroller.
If the Ethernet PHY is used, the crystal resonator X2 must be chosen as STM32 clock
source.
The clock source for the PHY is the clock output MCO signal of the STM32 microcontroller.
To operate in MII mode, the MCO signal must be configured to output 25 MHz, for RMII,
50 MHz.
By default the MII address of the Ethernet PHY is 0x01 and the initial configuration of the
Ethernet PHY is selected as shown in
Table 2
.
There are two LEDs embedded in RJ45 connector (CN5) which are used to indicate the
status of the line:
●
The green LED in the connector is switched on continuously when the Ethernet link is
established with the counterpart.
●
The yellow LED in the connector blinks when a transmission or a reception is ongoing.
The “Serial Management Interface” (SMI) is part of the MII interface and is used to transfer
management information between MAC and PHY (access of the PHY registers).
The PHY can communicate with the STM32 microcontroller over MII or RMII. SB1, SB2 and
SB3 must be configured according to the mode chosen. MII is chosen as a default option.
Table 2.
Default configuration of the Ethernet PHY
Function
Default configuration
Auto negotiation
Enabled
10/100 Mb
100 Mb selected for auto negotiation advertisement
Half/full duplex
Full duplex selected for auto negotiation advertisement
Internal loopback
Disabled
Power-down
Disabled (PHY is not in power-down)
MII/RMII mode
MII selected
Table 3.
Ethernet PHY configuration defined by SB1, SB2 and SB3
Function
MII
RMII
SB1
Removed
Fit 0
Ω
resistor
SB2
Removed
Fit 0
Ω
resistor
SB3
Fit 0
Ω
resistor
Removed
electronic components distributor
