Atmel SAM9X25, Manual

Page: 1049 / 1145

1049
11054A–ATARM–27-Jul-11
SAM9X25
1049
11054A–ATARM–27-Jul-11
SAM9X25
The MDIO interface can read IEEE 802.3 clause 45 PHYs as well as clause 22 PHYs. To read
clause 45 PHYs, bits[31:28] should be written as 0x0011. For a description of MDC generation,
see the network configuration register in the
“Network Control Register” on page 1055 .
45.4.13 Physical Interface
Depending on products, the Ethernet MAC is capable of interfacing to RMII or MII Interface. The
RMII bit in the EMAC_USRIO register controls the interface that is selected. When this bit is set,
the RMII interface is selected, else the MII interface is selected.
The MII and RMII interfaces are capable of both 10 Mb/s and 100 Mb/s data rates as described
in the IEEE 802.3u standard. The signals used by the MII interface are described in
Table 45-6 .
The intent of the RMII is to provide a reduced pin count alternative to the IEEE 802.3u MII. It
uses 2 bits for transmit (ETX0 and ETX1) and two bits for receive (ERX0 and ERX1). There is a
Transmit Enable (ETXEN), a Receive Error (ERXER), a Carrier Sense (ECRS_DV), and a 50
MHz Reference Clock (ETXCK_EREFCK) for 100Mb/s data rate.
45.4.13.1 RMII Transmit and Receive Operation
The same signals are used internally for both the RMII and the MII operations. The RMII maps
the signals in a more pin-efficient manner. The transmit and receive bits are converted from a 4-
bit parallel format to a 2-bit parallel scheme that is clocked at twice the rate. The carrier sense
and data valid signals are combined into the ECRSDV signal. This signal contains information
on carrier sense, FIFO status, and validity of the data. Transmit error bit (ETXER) and collision
detect (ECOL) are not used in RMII mode.
Table 45-6. Pin Configuration
Pin Name MII
ETXCK_EREFCK ETXCK: Transmit Clock
ECRS ECRS: Carrier Sense
ECOL ECOL: Collision Detect
ERXDV ERXDV: Data Valid
ERX0 - ERX3 ERX0 - ERX3: 4-bit Receive Data
ERXER ERXER: Receive Error
ERXCK ERXCK: Receive Clock
ETXEN ETXEN: Transmit Enable
ETX0-ETX3 ETX0 - ETX3: 4-bit Transmit Data
ETXER ETXER: Transmit Error