Overview
MPC5200B Users Guide, Rev. 1
Freescale Semiconductor 14-1
Chapter 14 Fast Ethernet Controller (FEC )

14.1 Overview

The fast Ethernet controller (FEC) is an Ethernet MAC plus two 1 Kbyte FIFOs that work under the control of the processor and BestComm
DMA engine to support 10/100 Mbps Ethernet/802.3 networks. Table 14-1 shows a block diagram.
A brief introduction and overview of the major functional blocks aid in understanding and programming the FEC.
The FEC is controlled by writing through the system interface (SIF) module into control registers located in each block. The control/status
register (CSR) block provides global control and interrupt handling registers. User programming of the CSR is the primary focus of this
chapter.
The RISC based Ethernet controller provides the following functions:
• Initialization
Address recognition for receive frames
Random number generation for transmit collision backoff timer
The FIFO controller is the focal point of all data flow in the FEC. The FIFO is divided into a transmit and receive FIFO of 1Kbyte each.
Transmit data flows from the CommBus into the transmit FIFO and through the transmit block to the physical layer device (PHY). Receive
data flows from the PHY to the receive block and is pulled out of the FIFO by BestComm. BestComm data transfers are interrupt driven.
Interrupt driven data movement from the processor is not supported.
The bus controller decides which block is to be the T-bus master for each cycle. All the blocks receive their control information over the T-bus
and provide status information over this same internal bus.
The media independent interface (MII) block provides a serial channel for control/status communication with the external physical layer
device (transceiver or PHY). The serial channel consists of the MDC (clock) and MDIO (bidirectional data I/O) lines of the MII interface.
The transmit and receive blocks provide the Ethernet MAC functionality (with some assistance from the BestComm unit). Internal to these
blocks are clock domain boundaries between the system clock and the network clocks supplied by the PHY.
The management information base (MIB) block maintains the counters for a variety of network events and statistics. The counters support the
RMON (RFC 1757) Ethernet statistics group and some of the IEEE 802.3 counters.
The FEC supports several standard MAC-PHY interfaces to connect to an external Ethernet transceiver. One is the 10/100 Mbps MII (18-wire)
interface. Another is the 10-Mbps only 7-Wire interface, which uses a subset of the MII pins.