Rainbow Electronics AT91CAP9S250A - Manual (Page 802)

802
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
42.3.12 Media Independent Interface
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 42-5 .
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.
42.3.12.1 RMII Transmit and Receive Operation
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.
Table 42-5. Pin Configuration
Pin Name MII RMII
ETXCK_EREFCK ETXCK: Transmit Clock EREFCK: Reference Clock
ECRS ECRS: Carrier Sense
ECOL ECOL: Collision Detect
ERXDV ERXDV: Data Valid ECRSDV: Carrier Sense/Data Valid
ERX0 - ERX3 ERX0 - ERX3: 4-bit Receive Data ERX0 - ERX1: 2-bit Receive Data
ERXER ERXER: Receive Error ERXER: Receive Error
ERXCK ERXCK: Receive Clock
ETXEN ETXEN: Transmit Enable ETXEN: Transmit Enable
ETX0-ETX3 ETX0 - ETX3: 4-bit Transmit Data ETX0 - ETX1: 2-bit Transmit Data
ETXER ETXER: Transmit Error