VSC7440 datasheet(51/444 Pages) MICROSEMI

51 / 444 page

Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

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.

3.8.5

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.

3.8.6

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

for power-sensitive applications. It uses a signal detect function that monitors the media interface for the

presence of a link to determine when to automatically power-down the PHY. The PHY “wakes up” at a

programmable interval and attempts to wake-up the link partner PHY by sending a burst of FLP over

copper media.

The ActiPHY power management mode in the integrated transceivers is enabled on a per-port basis

during normal operation at any time by setting PHY_AUX_CTRL_STAT.ACTIPHY_ENA to 1.

Three operating states are possible when ActiPHY mode is enabled:

•

Low power state

•

LP wake-up state

•

Normal operating state (link up state)

The PHY switches between the low power state and the LP wake-up state at a programmable rate (the

default is two seconds) until signal energy is detected on the media interface pins. When signal energy is

detected, the PHY enters the normal operating state. If the PHY is in its normal operating state and the

link fails, the PHY returns to the low power state after the expiration of the link status time-out timer. After

reset, the PHY enters the low power state.

When auto-negotiation is enabled in the PHY, the ActiPHY state machine operates as described. If auto-

negotiation is disabled and the link is forced to use 10BT or 100BTX modes while the PHY is in its low

power state, the PHY continues to transition between the low power and LP wake-up states until signal

energy is detected on the media pins. At that time, the PHY transitions to the normal operating state and

stays in that state even when the link is dropped. If auto-negotiation is disabled while the PHY is in the

normal operation state, the PHY stays in that state when the link is dropped and does not transition back

to the low power state.

The following illustration shows the relationship between ActiPHY states and timers.

VSC7440 датащи(PDF) 51 Page - Microsemi Corporation