VSC8658 datasheet(19/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

Figure 6 •

Automatic Media Sense Block Diagram

When both SerDes and Cat5 media interfaces attempt to establish a link, the preferred media interface

overrides a link-up of the non-preferred media interface. For example, if the preference is set for SerDes

mode and Cat5 media establishes a link, then Cat5 becomes the active media interface. However, after

the SerDes media interface establishes a link, the Cat5 interface drops its link because the preference

was set for SerDes mode. In this scenario, the SerDes preference determines the active media source

until the SerDes link is lost. Also, Cat5 media cannot link up unless there is no SerDes media link

established.

The following table lists the available AMS preferences.

The status of the media mode selected by the AMS can be read from device register 20E, bits 7:6. It

indicates whether copper media, SerDes media, or no media is selected.

Each PHY has two auto-media sense modes. The difference between the modes is based on the SerDes

media modes:

•

SerDes with Auto-Negotiation

•

SerDes with Pass-Through

For more information about SerDes media mode functionality with AMS enabled, see SerDes Media

Interface, page 10.

For AMS with SerDes auto-negotiation, the status and control of both the Cat5 and the SerDes media

can be made using registers 0 through 15. For AMS with SerDes pass-through, only the Cat5 interface

can have its interface control and status monitored. The SerDes media must then be controlled and

monitored within the MAC.

4.5

Cat5 Auto-Negotiation

The VSC8658 device supports twisted pair auto-negotiation as defined by clause 28 of the IEEE

standard 802.3-2000.

The auto-negotiation process consists of the evaluation of the advertised capabilities of the PHY and its

link partner to determine the best possible operating mode, throughput speed, duplex configuration, and

master or slave operating modes in the case of 1000BASE-T setups. Auto-negotiation also allows a

Table 3 •

AMS Media Preferences

Preference

Setting

Cat5 Linked,

Fiber Not Linked

SerDes Linked,

Cat5 Not Linked

Cat5 Linked,

SerDes Attempts

to Link

SerDes Linked,

Cat5 Attempts to

Link

Both Cat5 and

SerDes Attempt

to Link

SerDes

Cat5

SerDes

Cat5

SerDes

Cat5

Auto Sense

Logic

Cat5

Fiber Optic

Module

MAC

VSC8658 port_n

SIGDET

SerDes

SGMII /

Serial MAC

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