VSC8504-02 datasheet(27/131 Pages) MICROSEMI

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Functional Descriptions

VMDS-10507 VSC8504-02 Datasheet Revision 4.2

100BASE-T, and 1000BASE T). Known as HP Auto-MDIX, the function is fully compliant with Clause 40

of IEEE 802.3-2008.

Additionally, the device detects and corrects polarity errors on all MDI pairs — a useful capability that

exceeds the requirements of the standard.

Both HP Auto-MDIX detection and polarity correction are enabled in the device by default. Default

settings can be changed using device register bits 18.5:4. Status bits for each of these functions are

located in register 28.

Note: The VSC8504-02 can be configured to perform HP Auto-MDIX, even when autonegotiation is disabled

and the link is forced into 10/100 speeds. To enable this feature, set register 18.7 to 0. To use the

feature, also set register 0.12 to 0.

The HP Auto-MDIX algorithm successfully detects, corrects, and operates with any of the MDI wiring pair

combinations listed in the following table, which shows that twisted pair A (of four twisted paris A, B, C,

and D) is connected to the RJ45 connector 1,2 in normal MDI mode.

3.5.4

Manual HP Auto-MDIX Setting

As an alternative to HP Auto-MDIX detection, the PHY can be forced to be MDI or MDI-X using register

19E1, bits 3:2. Setting these bits to 10 forces MDI and setting 11 forces MDI-X. Leaving the bits 00

enables the HP Auto-MDIX setting to be based on register 18, bits 7 and 5.

3.5.5

Link Speed Downshift

For operation in cabling environments that are incompatible with 1000BASE-T, the VSC8504-02 provides

an automatic link speed downshift option. When enabled, the device automatically changes its

1000BASE-T autonegotiation advertisement to the next slower speed after a set number of failed

attempts at 1000BASE-T. No reset is required to get out of this state when a subsequent link partner with

1000BASE-T support is connected. This feature is useful in setting up in networks using older cable

installations that include only pairs A and B, and not pairs C and D.

To configure and monitor link speed downshifting, set register 20E1, bits 4:1. For more information, see

Table 29, page 51.

3.5.6

Energy Efficient Ethernet

The VSC8504-02 supports the IEEE 802.3az-2010 Energy Efficient Ethernet standard. This standard

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

uses low power idles (LPI) to achieve this objective.

Figure 18 •

Low Power Idle Operation

Table 3 •

Supported MDI Pair Combinations

RJ45 Connections

1, 2

3, 6 4, 5 7, 8

Mode

Normal MDI

Normal MDI-X

Normal MDI with pair swap on C and D pair

Normal MDI-X with pair swap on C and D pair

Active

Quiet

Low Power Idle

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