SAM7X256_14 Datasheet, PDF (544/662 Pages) ATMEL Corporation – ARM-based Flash MCU

37.3.11 PHY Maintenance
The register EMAC_MAN enables the EMAC to communicate with a PHY by means of the MDIO interface. It is used
during auto-negotiation to ensure that the EMAC and the PHY are configured for the same speed and duplex
configuration.
The PHY maintenance register is implemented as a shift register. Writing to the register starts a shift operation which is
signalled as complete when bit two is set in the network status register (about 2000 MCK cycles later when bit ten is set
to zero, and bit eleven is set to one in the network configuration register). An interrupt is generated as this bit is set.
During this time, the MSB of the register is output on the MDIO pin and the LSB updated from the MDIO pin with each
MDC cycle. This causes transmission of a PHY management frame on MDIO.
Reading during the shift operation returns the current contents of the shift register. At the end of management operation,
the bits have shifted back to their original locations. For a read operation, the data bits are updated with data read from
the PHY. It is important to write the correct values to the register to ensure a valid PHY management frame is produced.
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 550.
37.3.12 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 interface 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 37-5.
Table 37-5. 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
RMII
EREFCK: Reference Clock
ECRSDV: Carrier Sense/Data Valid
ERX0 - ERX1: 2-bit Receive Data
ERXER: Receive Error
ETXEN: Transmit Enable
ETX0 - ETX1: 2-bit Transmit Data
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.
37.3.12.1 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.
SAM7X Series [DATASHEET]
6120K–ATARM–11-Feb-14
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