8101 Datasheet, PDF(60/172 Page) LSI Computer Systems

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8101 Datasheet, PDF (60/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

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2.15.4 AutoNegotiation Enable

Setting the AN_EN bit in âRegister 9âConï¬guration 3â" Section 4.3.10,

enables the AutoNegotiation algorithm. When AutoNegotiation is

disabled the transmitter will output /I/ ordered sets.

2.15.5 Link Indication

The successful completion of the AutoNegotiation process (and by

deï¬nition the receiver has also acquired word synchronization) is

indicated by asserting the LINKn pin LOW, and setting the LINK bit in

âRegister 11âStatus 1â" Section 4.3.12. The LINK output pin can drive an

LED from VCC or GND as well as drive another digital input.

2.16 Flow Control

Flow control causes a remote station to temporarily halt sending packets

in order to prevent packet loss in a congested system. The controller

uses MAC control frames for ï¬ow control, according to IEEE 802.3x

speciï¬cations. Refer to Section 2.17, âMAC Control Framesâ for more

details on the MAC control frame ï¬ow control scheme.

2.17 MAC Control Frames

MAC control frames are packets that pass signaling information between

stations and are speciï¬ed in IEEE 802.3, Clause 31. MAC control frames

are used primarily for ï¬ow control.

MAC control frames are differentiated from other packets because they

have the unique value of 0x8808 in the length/type ï¬eld. MAC control

frames have the same format as normal Ethernet packets, except the

data ï¬eld, consists of an opcode ï¬eld and a parameter ï¬eld. The opcode

ï¬eld contains an opcode command and the parameter ï¬eld contains a

value associated with the opcode command. The only opcode command

deï¬ned to date by IEEE 802.3x is the pause opcode; the parameter ï¬eld

for the pause opcode deï¬nes the pause time. MAC control frames with

the pause opcode, referred to as pause frames, are only allowed to have

a destination address equal to a speciï¬c reserved multicast address or

the address of the receive station itself. The value of the reserved

multicast address is 0x0180C2000001.

2-42

Functional Description

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