at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 632

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

36.3.13
Table 36-5.
36.3.13.1
632
Pin Name
ETXCK_EREFCK
ECRS
ECOL
ERXDV
ERX0 - ERX3
ERXER
ERXCK
ETXEN
ETX0-ETX3
ETXER
AT91SAM9G20 Preliminary
Media Independent Interface
RMII Transmit and Receive Operation
Pin Configuration
The Ethernet MAC is capable of interfacing to both RMII and MII Interfaces. The RMII bit in the
EMAC_USRIO register controls the interface that is selected. When this bit is set, the RMII inter-
face is selected, else the MII interface is selected.
The MII and RMII interface are capable of both 10Mb/s and 100Mb/s data rates as described in
the IEEE 802.3u standard. The signals used by the MII and RMII interfaces are described in
Table
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.
The same signals are used internally for both the RMII and the MII operations. The RMII maps
these 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.
ERX0 - ERX3: 4-bit Receive Data
ETX0 - ETX3: 4-bit Transmit Data
36-5.
ETXEN: Transmit Enable
ETXCK: Transmit Clock
ERXCK: Receive Clock
ECOL: Collision Detect
ERXER: Receive Error
ETXER: Transmit Error
ECRS: Carrier Sense
ERXDV: Data Valid
MII
ECRSDV: Carrier Sense/Data Valid
ERX0 - ERX1: 2-bit Receive Data
ETX0 - ETX1: 2-bit Transmit Data
EREFCK: Reference Clock
ETXEN: Transmit Enable
ERXER: Receive Error
RMII
6384B–ATARM–15-Dec-08