VSC8658 datasheet(23/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

4.11

IEEE 802.3af PoE Support

The VSC8658 device is also compatible with switch 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 clause 33 of the IEEE standard 802.3af.

4.12

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 such as laptop computers with Wake-on-LAN™ capability. 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 VSC8658 device is enabled on a per-port basis during

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

There are three operating states possible when ActiPHY™ mode is enabled:

•

Low power state

•

LP wake-up state

•

Normal operating state (link up state)

The VSC8658 device 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 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.

Figure 8 •

ActiPHY State Diagram

4.12.1

Low Power State

In the low power state, all major digital blocks are powered down. However, the following functionality is

provided:

•

SMI interface (MDC, MDIO, MDINT_n)

Timeout Timer Expires;

Auto-negotiation Enabled

FLP Burst or

Clause 37 Restart

Signal Sent

Low Power State

Normal

Operation

Link Partner

Wake-up State

Signal Energy

Detected on the

Connected Media

Sleep Timer

Expires

VSC8658 Datasheet(PDF) 23 Page - Microsemi Corporation

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