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DM8108

8 port 10/100M Fast Ethernet Switching Controller

Davicom Semiconductor, Inc. 

DM8108

8 port 10/100M Fast Ethernet Switching Controller

Functional Description

Fast Ethernet Ports Functional Overview

The DM8108 is a high-performance, low-cost Fast

Ethernet Switching Controller which provides packet

switching between eight on-chip, 10/100 Mbps ports

and one optional expansion port. It is suitable for the

auto-sensing 10/100Mbps switch application.

Switching Architecture

The switching architecture is based on the shared memory

and handshaking signals to switch packets between on-chip

ports hard-wired.

For an incoming packet, the receiving port’s MAC stores it in

the receiving buffers if it is a good packet. At the same

time, the switching engine determines which port the packet

will forward to and update the address table which will be

used for future packet forwarding reference.

Fast Ethernet Ports

The DM8108 integrates eight Fast Ethernet ports, working

at 10/100Mbps (half-duplex) or 20/200Mbps (full-duplex)

with off-the-shelf PHY chips. The interface is glue-less

through Media Independent Interfaces (MII). The auto-

negotiation function determines the port’s operating mode.

With auto-negotiation disabled, the ports can be forced to

operate at a certain mode, if so desired. Each port includes

the Media Access Control function (MAC), LED signals for

Link, Collision, Receive/Transmit, Half/Full duplex and

Receive Buffer Full indications.

Address Recognition

The DM8108 in a system can recognize up to 16K Uni-cast

MAC addresses and unlimited Multicast/Broadcast MAC

addresses. An intelligent address recognition mechanism

enables filtering and forwarding packets at full Ethernet wire

speed. The DM8108 provides an address self-learning

mechanism. As each DM8108 learns new address, it

updates the address table in the storage.

Fig.1: Typical 10/100 Mbps auto-sensing switching hub application

MEM

MEM

DM8108

optional

DM8108

10/100 Mbps PHY

Switch Ports

10/100 Mbps PHY

Switch Ports

10

Preliminary

Version: DM8108-DS-P02

November 25, 1999

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