VSC7440 datasheet(48/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

duplex mode. Note that while 10BASE-T and 100BASE-T do not require auto-negotiation, 1000BASE-T

does require it (defined by clause 40).

3.8.2.3

1000BASE-T Forced Mode Support

The integrated transceivers provides support for a 1000BASE-T forced test mode. In this mode, the PHY

can be forced into 1000BASE-T mode and does not require manual setting of master/slave at the two

ends of the link. This mode is only for test purposes. Do not use in normal operation. To configure a PHY

in this mode, set PHY_EEE_CTRL.FORCE_1000BT_ENA = 1, with

PHY_CTRL.SPEED_SEL_LSB_CFG = 1 and PHY_CTRL.SPEED_SEL_LSB_CFG = 0.

3.8.2.4

Automatic Crossover and Polarity Detection

For trouble-free configuration and management of Ethernet links, the integrated transceivers include a

robust automatic crossover detection feature for all three speeds on the twisted-pair interface

(10BASE-T, 100BASE-T, and 1000BASE-T). Known as HP Auto-MDIX, the function is fully compliant

with clause 40 of the IEEE 802.3-2002.

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 the POL_INV_DIS and PAIR_SWAP_DIS fields in the

PHY_BYPASS_CTRL register. Status bits for each of these functions are located in the

PHY_AUX_CTRL_STAT register.

The integrated transceivers can be configured to perform HP Auto-MDIX, even when auto-negotiation is

disabled (PHY_CTRL.AUTONEG_ENA = 0) and the link is forced into 10/100 speeds. To enable the HP

Auto-MDIX feature, set PHY_BYPASS_CTRL.FORCED_SPEED_AUTO_MDIX_DIS 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.

3.8.2.5

Manual MDI/MDI-X Setting

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

PHY_EXT_MODE_CTRL.FORCE_MDI_CROSSOVER_ENA. Setting this field to 10 forces MDI, and

setting 11 forces MDI-X. Leaving the bits 00 enables the MDI/MDI-X setting to be based on

FORCED_SPEED_AUTO_MDIX_DIS and PAIR_SWAP_DIS in the register PHY_BYPASS_CTRL.

3.8.2.6

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.

Table 8 •

Supported MDI Pair Combinations

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

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