DM8108 Ver la hoja de datos (PDF) - Unspecified

Número de pieza

componentes Descripción

Lista de partido

DM8108

8 port 10/100M Fast Ethernet Switching Controller

Unspecified 

DM8108

8 port 10/100M Fast Ethernet Switching Controller

Auto-Negotiation

Auto-negotiation disabled

When ANEG* (MA[7:0]) strap pin is high, auto-

negotiation is disabled, and the corresponding port

can be selected as half- or full- duplex mode

respectively. Following the RESET the port duplex

mode is set by the state sampled on the TXEN(7:0)

pins. The speed that each port operates in (10Mbps

or 100Mbps) is determined by the frequency of

TxCLK(7:0) and RxCLK(7:0) generated by PHY. The

PHY generates 25MHz clock for both TxCLK and

RxCLK in 100Mbps operation and 2.5MHz clock in

10Mbps operation.

Auto-negotiation enabled

When ANEG* (MA[7:0]) pins are tied low, the MAC

decodes the duplex mode from the values of the

Auto-Negotiation Advertisement Register and the

Auto-Negotiation Link Partner Ability Register at the

end of Auto-negotiation process. Once the duplex

mode is resolved, the DM8108 updates the port

control registers. The DM8108 will continuously

perform the following operations for each port (PHY

address 0-7 alternatively), implemented as READ

commands issued via the MDCLK/MDIO interface:

Link Detection and Link Detection Bypass

(FLNK*)

The DM8108 will continuously query the PHY devices

for their link status associated with Auto-Negotiation

Process. The DM8108 will alternatively read

registers from PHY address 0 to 7 and update the

internal link bits according to the value of bit 2 of

register 1. In case of link down (bit 1.2=0), that port

will enter “link test fail state”. In this state, all the port’s

logic go to a reset state. The port will enter the “link

up state” if the bit 1.2 is “1” or the FLNK* (force link,

LEDSTB* strobed low during reset) pin is sampled low

during reset.

Partition Mode

A port enters partition mode when more than 64

consecutive collisions are seen on the port. In partition

mode the port continuous to transmit but it will not receive.

A port returned to normal operation mode when a good

packet is seen on the wire.

20

Enabling Partition Mode

Partitioned mode is enabled always.

Entering Partition State

A port will enter the Partition state when PAEN* strap pin

sampled low during reset and when either of the following

conditions occurs:

T The port detects a collision on every one of 64

consecutive re-transmit attempts to the same packet.

T The port detects a single collision which occurs for

more than 512 bit times.

While in Partition state:

T The port will continue to transmit its pending packet,

regardless of the collision detection, and will not allow

the usual Back-off Algorithm. Additional packets

pending for transmission, will be transmitted, while

ignoring the internal collision indication. This frees up

the port’s transmit buffers which would otherwise be

filled up at the expense of other ports buffers. The

assumption is that the partition is signifying a system

failure situation (bad connection/cable/station), thus

dropping packets is a small price to pay vs. the cost of

halting the switch due to a buffer full condition. The

partition indication is available via the LED interface.

Exiting from Partition State

The Port exits from Partition State, following the end of a

successful packet transmission. A successful packet

transmission is defined as no collisions were detected on the

first 512 bits of the transmission.

Expansion Bus

The expansion bus operates at Full-Duplex mode that

provides up-to 7200Mbps bandwidth for device to

device connection. Several DM8108 can be

cascaded as a pipe to provide a robust Ethernet

Switching system.

The bus itself is very simple. The transmit and receive ports

contain independent data, valid and handshake signals.

No bus arbitration is involved.

Preliminary

Version: DM8108-DS-P02

November 25, 1999

Share Link: