Espressif ESP32 Technical Reference Manual page 236

10 Ethernet Media Access Controller (MAC)
frame. This signal must be disabled before the first clock cycle following the last nibble. In order to re-
ceive the frame correctly, the MII_RX_DV signal must cover the frame to be received over the time range,
starting no later than when the SFD field appears.
• MII_CRS: Carrier sense signal. When the transmitting or receiving medium is in the non-idle state, the
signal is enabled by the PHY. When the transmitting or receiving medium is in the idle state, the signal
is disabled by the PHY. The PHY must ensure that the MII_CRS signal remains valid under conflicting
conditions. This signal does not need to be synchronized with the TX and RX clocks. In full-duplex mode,
this signal is insignificant.
• MII_COL: Collision detection signal. After a collision is detected on the medium, the PHY must immediately
enable the collision detection signal, and the collision detection signal must remain active as long as a
condition for collision exists. This signal does not need to be synchronized with the TX and RX clocks. In
full-duplex mode, this signal is meaningless.
• MII_RX_ER: Receive error signal. The signal must remain for one or more cycles (MII_RX_CLK) to indicate
to the MAC sublayer that an error has been detected somewhere in the frame.
• MDIO and MDC: Management Data Input/Output and Management Data Clock. The two signals constitute
a serial bus defined for the Ethernet family of IEEE 802.3 standards, used to transfer control and data
information to the PHY, see section
10.6.1.2 MII Clock
In MII mode, there are two directions of clock, Tx and Rx clocks in the interface between MII and the PHY.
MII_TX_CLK is used to synchronize the TX data, and MII_RX_CLK is used to synchronize the RX data. The
MII_RX_CLK clock is provided by the PHY. The MII_TX_CLK is provided by the chip's internal PLL or external
crystal oscillator. For details regarding Figure 10-4, please refer to the clock-related registers in
mary.
Espressif Systems
Station Management Agent (SMA)
Figure 10-4. MII Clock
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Interface.
Register Sum-
ESP32 TRM (Version 5.2)