Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
45-3
a runt or collided frame, with no DMA activity. However, external memory for buffers and BDs is
required; on-chip FIFOs are designed only to compensate for collisions and for system bus latency.
Independent TxBD and RxBD rings in external memory allow nearly unlimited flexibility in memory
management of transmit and receive data frames. External memory is inexpensive, and because BD rings
in external memory have no inherent size limitations, memory management can be easily optimized to
system needs.
45.2
Fast Ethernet Controller Operation
This section discusses the operation of the FEC.
45.2.1
Transceiver Connection
The FEC supports both an MII or RMII interface for 10/100 Mbps Ethernet and a seven-wire serial
interface for 10-Mbps Ethernet. The interface mode is selected by R_CNTRL[MII_MODE], described in
Section 45.3.2.20, “Receive Control Register (R_CNTRL).”
Table 45-2
shows the 18 MII and the 10 RMII
interface signals that are defined by the 802.3 standard.
Serial-mode connections to the external transceiver are shown in
Table 45-3
.
Table 45-2. MII and RMII Signals
Signal Description
FEC MII Signal Name
FEC RMII Signal Name
Transmit clock
TX_CLK
REFCLK
Transmit enable
TX_EN
TX_EN
Transmit data
TXD[3:0]
TXD[1:0]
Transmit error
TX_ER
Collision
COL
Carrier sense
CRS
Receive clock
RX_CLK
Receive enable
RX_DV
CRS_DV
Receive data
RXD[3:0]
RXD[1:0]
Receive error
RX_ER
RX_ER
Management channel clock
MDC
MDC
Management channel serial data
MDIO
MDIO
Table 45-3. Serial Mode Connections to the External Transceiver
Signal Description
FEC MII Signal Name
FEC MII Signal Name
Transmit clock
TX_CLK
REFCLK
Transmit enable
TX_EN
TX_EN
Transmit data
TXD0
TXDO
Summary of Contents for PowerQUICC MPC870
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