mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 227

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
The descriptor controller opens and closes the buffer descriptors. The DMA controller
manages the data transfer. As soon as the DMA channel is initialized, it begins transferring
data. An on-board RAM acts as both a transmit and receive FIFO, and also provides scratch
memory for the FEC.
The RAM is the focal point of all data flow in the FEC. The RAM is divided into three
sections: transmit FIFO, receive FIFO, and descriptor controller memory. User data flows
to or from the DMA unit from or to the receive/transmit FIFOs. Transmit data flows from
the transmit FIFO into the transmit block. Receive data flows from the receive block into
the receive FIFO.
The user controls the FEC by writing into control registers located in each block. The
control and status registers (CSRs) provide global control (for example, Ethernet reset and
enable) and interrupt handling. The MII block provides a serial channel for the FEC and
external physical layer device to pass control and status information.
The descriptor controller manages data flow in both transmit and receive directions. It is
programmed with microcode to open and close buffer descriptors, control the transmit
collision recovery process, and filter received frame addresses.
The descriptor controller accesses both the transmit and receive descriptor rings through the
descriptor access block. The descriptor access block acts as a dedicated single channel
DMA that either reads a descriptor in external user memory or writes an updated descriptor
back into user memory.
11.3 Transceiver Connection
The FEC supports both an MII interface for 10/100 Mbps Ethernet and a seven-wire serial
interface for 10 Mbps Ethernet. The interface mode is selected by RCR[MII_MODE]. In
MII mode, the 802.3 standard defines and the FEC module supports 18 signals. These are
shown in Table 11-1.
Transmit clock
Transmit enable
Transmit data
Transmit error
Collision
Carrier sense
Receive clock
Receive enable
Receive data
Receive error
Signal Description
Chapter 11. Ethernet Module
Table 11-1. MII Mode
MCF5272 Pin
E_RxD[3:0]
E_TxD[3:0]
E_RxCLK
E_TxCLK
E_TxEN
E_TxER
E_RxDV
E_RxER
E_COL
E_CRS
Transceiver Connection
11-3