VSC8504-02 datasheet(32/131 Pages) MICROSEMI

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Functional Descriptions

VMDS-10507 VSC8504-02 Datasheet Revision 4.2

3.9

IEEE 802.3af PoE Support

The VSC8504-02 device is compatible with designs that are 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 IEEE

802.3af Clause 33.

3.10

ActiPHY Power Management

In addition to the IEEE-specified power-down control bit (device register bit 0.11), the device also

includes an ActiPHY power management mode for each PHY. This mode enables support for power-

sensitive applications. It utilizes 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 VSC8504-02 is enabled on a per-port basis during normal

operation at any time by setting register bit 28.6 to 1.

The following operating states are possible when ActiPHY mode is enabled:

•

Low power state

•

Link partner wake-up state

•

Normal operating state (link-up state)

The VSC8504-02 switches between the low power state and LP wake-up state at a programmable rate

(the default is two seconds) until signal energy has been 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 autonegotiation is enabled in the PHY, the ActiPHY state machine operates as described. When

autonegotiation is disabled and the link is forced to use 10BASE-T or 100BASE-TX 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. When autonegotiation 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.

Figure 25 •

ActiPHY State Diagram

Low Power State

LP Wake-up

State

Normal

Operation State

Signal Energy Detected on

Media

Timeout Timer Expires and

Auto-negotiation Enabled

Sleep Timer Expires

FLP Burst or

Clause 37 Restart

Signal Sent

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