DM8108
8 port 10/100M Fast Ethernet Switching Controller
10
Preliminary
Version: DM8108-DS-P02
November 25, 1999
optional
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, ifso 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
Switch Ports
Switch Ports
DM8108
10/100 Mbps PHY
MEM
MEM
DM8108
10/100 Mbps PHY
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