STM32F101xx, STM32F102xx, STM32F103xx, STM32F105xx and ...

Ethernet (ETH): media access control (MAC) with DMA controller
RM0008
Figure 287. MDIO timing and frame structure - Read cycle
MDC
MDIO 32 1's 0 1 1 0 A4 A3 A2 A1 A0 R4 R3 R2 R1 R0 D15 D14 D1 D0
Preamble
Start
of
frame
OP
code
PHY address Register address Turn
around
data
Data to PHY
Data from PHY
ai15627
SMI clock selection
The MAC initiates the Management Write/Read operation. The SMI clock is a divided clock
whose source is the application clock (AHB clock). The divide factor depends on the clock
range setting in the MII Address register.
Table 190 shows how to set the clock ranges.
Table 190.
Clock range
Selection AHB clock MDC clock
0000 60-72 MHz AHB clock / 42
0001 Reserved -
0010 20-35 MHz AHB clock / 16
0011 35-60 MHz AHB clock / 26
0100, 0101, 0110, 0111 Reserved -
27.4.2 Media-independent interface: MII
The media-independent interface (MII) defines the interconnection between the MAC
sublayer and the PHY for data transfer at 10 Mbit/s and 100 Mbit/s.
844/995 Doc ID 13902 Rev 9