VSC7511 datasheet(55/324 Pages) MICROSEMI

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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

Figure 13 •

Inline Powered Ethernet Switch

The following procedure describes the process that an Ethernet switch must perform to process inline power requests

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

Enables the inline powered device detection mode on each transceiver using its serial management

interface. Set PHY_CTRL_EXT4.INLINE_POW_DET_ENA to 1.

Ensures that the 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

PHY_CTRL_EXT4.INLINE_POW_DET_STAT returns 00 during the search for devices that require

Power-over-Ethernet (PoE).

The transceiver 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 PHY_CTRL_EXT4.INLINE_POW_DET_STAT reads back 01. If an LP device does not loop

back the FLP after a specific time, PHY_CTRL_EXT4.INLINE_POW_DET_STAT automatically

resets to 10.

If the transceiver 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

PHY_CTRL_EXT4.INLINE_POW_DET_STAT 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 (PHY_STAT.LINK_STAT is set to 1).

In the event of a link failure (indicated when PHY_STAT.LINK_STAT reads 0), the inline power must

be disabled to the inline powered device external to the PHY. The transceiver disables its normal

auto-negotiation process and re-enables its inline powered device detection mode.

3.5.5

IEEE 802.3af PoE Support

The integrated transceivers are also compatible with switch designs intended for use in systems that

supply power to Data Terminal Equipment (DTE) by means of the MDI or twisted pair cable, as described

in clause 33 of the IEEE 802.3af.

3.5.6

ActiPHY™ Power Management

In addition to the IEEE-specified power-down control bit (PHY_CTRL.POWER_DOWN_ENA), the device

also includes an ActiPHY power management mode for each PHY. The ActiPHY mode enables support

Control

PHY_port1

Inline,

Power-Over-Ethernet (PoE)

Power Supply

Cat5

PHY_port0

PHY_portn

Transformer

RJ-45

I/F

Transformer

RJ-45

I/F

Transformer

RJ-45

I/F

Link

Partner

Link

Partner

Link

Partner

Gigabit Switch/PHY

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