DocID13902 Rev 15 968/1128
RM0008 Ethernet (ETH): media access control (MAC) with DMA controller
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Figure 331. MII clock sources
29.4.3 Reduced media-independent interface: RMII
The reduced media-independent interface (RMII) specification reduces the pin count
between the microcontroller Ethernet peripheral and the external Ethernet in 10/100 Mbit/s.
According to the IEEE 802.3u standard, an MII contains 16 pins for data and control. The
RMII specification is dedicated to reduce the pin count to 7 pins (a 62.5% decrease in pin
count).
The RMII is instantiated between the MAC and the PHY. This helps translation of the MAC’s
MII into the RMII. The RMII block has the following characteristics:
• It supports 10-Mbit/s and 100-Mbit/s operating rates
• The clock reference must be doubled to 50 MHz
• The same clock reference must be sourced externally to both MAC and external
Ethernet PHY
• It provides independent 2-bit wide (dibit) transmit and receive data paths
Figure 332. Reduced media-independent interface signals
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