VSC8658 datasheet(22/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

Figure 7 •

Inline Powered Ethernet Switch Diagram

The following procedure describes the process that an Ethernet switch must perform in order to process

inline power requests made by a link partner (LP) that is, in turn, capable of receiving inline power.

Enable the inline powered device detection mode on each VSC8658 PHY using its serial

management interface. Set register bit 23E.10 to 1.

Ensure that the VSC8658 device Auto-Negotiation Enable bit (register 0.12) is also set to 1. In the

application, the device sends a special Fast Link Pulse (FLP) signal to the LP. Reading register bit

23E.9:8 returns 00 during the search for devices that require Power-over-Ethernet (PoE).

The VSC8658 PHY monitors its inputs for the FLP signal looped back by the LP. An LP capable of

receiving PoE loops back the FLP pulses when the LP is in a powered-down state. This is reported

when VSC8658 device register bit 23E.9:8 reads back 01. It can also be verified as an inline power

detection interrupt by reading VSC8658 device register bit 26.9, which should be a 1, and which is

subsequently cleared and the interrupt de-asserted after the read. If an LP device does not loop

back the FLP after a specific time, VSC8658 device register bit 23E.9:8 automatically resets to 10.

If the VSC8658 PHY reports that the LP needs PoE, the Ethernet switch must enable inline power

on this port, externally of the PHY.

The PHY automatically disables inline powered device detection if the VSC8658 device register bit

23E.9:8 automatically resets to 10, and then automatically changes to its normal auto-negotiation

process. A link is then auto-negotiated and established when the link status bit is set (register bit 1.2

is set to 1).

In the event of a link failure (indicated when VSC8658 device register bit 1.2 reads 0), the inline

power should be disabled to the inline powered device external to the PHY. The VSC8658 PHY

disables its normal auto-negotiation process and re-enables its inline powered device detection

mode.

SMI

Control

Processor

VSC8658_1

SGMII

Interface

Inline,

Power-Over-Ethernet

(PoE)

Power Supply

Cat5

Gigabit Switch

VSC8658_0

VSC8658_n

Transformer

RJ-45

I/F

Transformer

RJ-45

I/F

Transformer

RJ-45

I/F

Link

Partner

Link

Partner

Link

Partner

VSC8658 Datasheet(PDF) 22 Page - Microsemi Corporation

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