MII_TXCLK
MII_TXD[3−0]
MII_TXEN
MII_COL
MII_CRS
MII_RXCLK
MII_RXD[3−0]
MII_RXDV
MII_RXER
MDIO_CLK
MDIO_D
Physical
layer
device
(PHY)
System
core
Transformer
2.5 MHz
or
25 MHz
RJ−45
EMAC
MDIO
Architecture
715
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
EMAC/MDIO Module
The MII interface frequencies for the transmit and receive clocks are fixed by the IEEE 802.3 specification
as:
•
2.5 MHz at 10 Mbps
•
25 MHz at 100 Mbps
The RMII interface frequency for the transmit and receive clocks are fixed at 50 MHz for both 10 Mbps
and 100 Mbps.
18.2.2 Memory Map
The EMAC peripheral includes internal memory that is used to hold buffer descriptions of the Ethernet
packets to be received and transmitted. This internal RAM is 2K × 32 bits in size. Data can be written to
and read from the EMAC internal memory by either the EMAC or the CPU. It is used to store buffer
descriptors that are 4-words (16-bytes) deep. This 8K local memory holds enough information to transfer
up to 512 Ethernet packets without CPU intervention. This EMAC RAM is also referred to as the CPPI
buffer descriptor memory because it complies with the Communications Port Programming Interface
(CPPI) v3.0 standard.
The packet buffer descriptors can also be placed in other on- and off-chip memories such as L2 and
EMIF. There are some tradeoffs in terms of cache performance and throughput when descriptors are
placed in the system memory, versus when they are placed in the EMAC’s internal memory. In general,
the EMAC throughput is better when the descriptors are placed in the local EMAC CPPI RAM.
18.2.3 Signal Descriptions
Support of interfaces (MII and/or RMII) varies between devices. See your device-specific data manual for
information.
18.2.3.1 Media Independent Interface (MII) Connections
shows a device with integrated EMAC and MDIO interfaced via a MII connection in a typical
system. The EMAC module does not include a transmit error (MTXER) pin. In the case of transmit error,
CRC inversion is used to negate the validity of the transmitted frame.
The individual EMAC and MDIO signals for the MII interface are summarized in
. For more
information, refer to either the IEEE 802.3 standard or ISO/IEC 8802-3:2000(E).
Figure 18-2. Ethernet Configuration—MII Connections