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DM8108

8 port 10/100M Fast Ethernet Switching Controller

Unspecified 

The receive port utilizes the RDVCLK to clock in the

received data into FIFO and uses RXTOG requests for a

Receiving Buffer block. The switching engine will execute

the similar process as for the Ethernet Ports.

DM8108

8 port 10/100M Fast Ethernet Switching Controller

The transmit port appends the Sync. field to a normal

Ethernet packet and sends the packet out through TD(3:0)

at the rising edge of TXENCLK.

TXENCLK

TD(3:0)

Nib n-1 NIb n

Nib n+1

Switching Engine

All the packet switching is processed by the Switching

Engine, which has following functions:

MAC Address Learning Process

The DM8108 has a self-learning mechanism for learning

the MAC addresses of attached Fast Ethernet devices in

real time. The DM8108 searches for the source address of

an incoming packet in the Address Table and acts as

follows:

If the source address was not found in the Address Table,

the DM8108 waits until the end of the packet (no error) and

updates the Address Table.

If the source address was found in the Address Table, the

DM8108 waits for a good packet received indication.

Address Recognition

The DM8108 forwards the incoming packets to appropriate

port(s) according to the Destination Address as follows:

T If the packet is from a local port--

1) If it is a Unicast address and the address is found

in the Address Table, the DM8108 will:

. If the port number recorded is matched to port

number on which the packet received, the packet

is discarded.

. If the port numbers are different, the packet is

forwarded to the appropriate port.

2) If it is a Unicast address and the address is not

found in the Address Table, the DM8108 acts as if

Preliminary

Version: DM8108-DS-P02

November 25, 1999

the packet is a Multicast packet and forwards it to

the Expansion Transmit port and all the local

ports except the incoming port,

3) If it is a Multicast/Broadcast address, the packet is

forwarded to the Expansion Transmit port and all

local ports (except to the port on which the packet

was received).

T If the packet is from Expansion Bus—

1) If it is a Unicast address specified in the

Destination Address in the Ethernet Packet, the

DM8108 will:

. If the recorded port pointed to a local port, the

packet will be forwarded to that port.

. If the destination address is not found (not

recorded by the Mac address learning process),

the packet will be forwarded to all the local ports

and the Expansion Transmit port.

2) If it is a Multicast/Broadcast address (destination

device # should set invalid), the packet will be

forwarded to all the local ports and the Expansion

Transmit port.

Address Aging

The DM8108 includes hardware to support for automatic

address aging.

Buffers and Queues

The DM8108 incorporates 3 transmit queues and one

common receive buffer area for the two Fast Ethernet ports

and the Expansion Port, The queues and buffers are

located in the DRAM along with Address Table. The

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