VSC7511 datasheet(53/324 Pages) MICROSEMI

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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

3.5.2.6

Link Speed Downshift

For operation in cabling environments that are incompatible with 1000BASE-T, the device provides an

automatic link speed “downshift” option. When enabled, the device automatically changes its 1000BASE-

T auto-negotiation advertisement to the next slower speed after a set number of failed attempts at

1000BASE-T. No reset is required to exit this state if a subsequent link partner with 1000BASE-T support

is connected. This is useful in setting up in networks using older cable installations that may include only

pairs A and B and not pairs C and D.

Link speed downshifting is configured and monitored using SPEED_DOWNSHIFT_STAT,

SPEED_DOWNSHIFT_CFG, and SPEED_DOWNSHIFT_ENA in the register PHY_CTRL_EXT3.

3.5.2.7

Energy Efficient Ethernet

The integrated transceivers support IEEE 802.3az Energy Efficient Ethernet (EEE). This standard

provides a method for reducing power consumption on an Ethernet link during times of low use.

Figure 11 •

Low Power Idle Operation

Using LPI, the usage model for the link is to transmit data as fast as possible and then return to a low

power idle state. Energy is saved on the link by cycling between active and low power idle states. Power

is reduced during LPI by turning off unused circuits and, using this method, energy use scales with

bandwidth utilization.

The transceivers use LPI to optimize power dissipation in 100BASE-TX and 1000BASE-T operation. In

addition, IEEE 802.3az defines a 10BASE-Te mode that reduces transmit signal amplitude from 5 V to

approximately 3.3 V, peak-to-peak. This mode reduces power consumption in 10 Mbps link speed and

can fully interoperate with legacy 10BASE-T compliant PHYs over 100 m Cat5 cable or better.

To configure the transceivers in 10BASE-Te mode, set PHY_EEE_CTRL.EEE_LPI_RX_100BTX_DIS to

1 for each port. Additional Energy Efficient Ethernet features are controlled through Clause 45 registers

as defined in Clause 45 registers to Support Energy Efficient Ethernet

3.5.3

Wake-On-LAN and SecureOn

The device supports Wake-on-LAN, an Ethernet networking standard to awaken hosts by using a “magic

packet” that is decoded to ascertain the source, and then assert an interrupt pin or an LED. The device

also supports SecureOn to secure Wake-on-LAN against unauthorized access. The following illustration

shows an overview of the Wake-on-LAN functionality.

Active

Low-Power Idle

Active

Quiet

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