VSC8658 datasheet(21/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

Note: The VSC8658 device can be configured to perform Auto MDI/MDI-X even when its Auto-negotiation

feature is disabled (setting register 0.12 to 0) and the link is forced into 10/100 speeds. To enable this

feature, set register 18.7 to 0.

4.8

Link Speed Downshift

For operation in cabling environments that are incompatible with 1000BASE-T, the VSC8658 device

provides an automatic link speed “downshift” option. When enabled, the device automatically changes its

1000BASE-T auto-negotiation advertisement to the next slower speed after a set number of failed

attempts at 1000BASE-T.

This is useful in setting up in networks using older cable installations that may include only pairs A and B

and not pairs C and D.

You can configure and monitor link speed downshifting using register bits 20E.4:1. For more information,

see Extended PHY Control Set 1, page 37.

4.9

Transformerless Ethernet

The Cat5 media interface supports 10/100/1000BT Ethernet for backplane applications such as those

specified by the PICMG™ 2.16 and ATCA™ 3.0 specifications for eight-pin channels. With proper AC

coupling, the typical Cat5 transformer can be removed and replaced with capacitors.

4.10

Ethernet Inline Powered Devices

The VSC8658 device can detect legacy inline powered devices in Ethernet network applications. Its

inline powered detection capability can be part of a system that allows for IP-phone and other devices

such as wireless access points to receive power directly from their Ethernet cable, similar to office digital

phones receiving power from a Private Branch Exchange (PBX) office switch over the telephone cabling.

This can eliminate the need for an IP-phone to have an external power supply. It also enables the inline

powered device to remain active during a power outage (assuming the Ethernet switch is connected to

an uninterrupted power supply, battery, back-up power generator, or some other uninterruptable power

source).

For more information about legacy inline powered device detection, visit the Cisco Web site at

www.cisco.com.

The following illustration shows an example of this type of application.

VSC8658 Datasheet(PDF) 21 Page - Microsemi Corporation