VSC8658 datasheet(18/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

4.2

SerDes Media Interface

The VSC8658 device SerDes Media Interface performs data serialization and deserialization functions

using an integrated SerDes block. The interface operates at 1.25 Gbps speed, providing full-duplex and

half-duplex 1000 Mbps bandwidth that can connect directly to 100BASE-FX/1000BASE-X-compliant

optical devices as well as to 10/100/1000BASE-T copper SFP devices. The interface can be operated in

two SerDes modes:

•

SerDes with Media Interface PCS Auto-Negotiation mode

•

SerDes with Pass-Through mode

The SerDes with Media Interface PCS Auto-Negotiation mode supports IEEE standard 802.3, clauses 36

and 37, which describe fiber auto-negotiation. In this mode, control and status of the SerDes media is

displayed in the VSC8658 device registers 0 through 15 in a manner similar to what is described in the

IEEE standard 802.3, clause 28. In this mode, connected copper SFPs can only operate at 1000BASE-T

speed. A link in this mode is established using auto-negotiation (enabled or disabled) between the PHY

and the link partner.

For information about how the VSC8658 LEDs operate in this mode, see LED Behavior, page 19.

SerDes with Pass-Through mode is a feature that links a fiber module or copper SFP directly to the

SerDes interface of the MAC through the VSC8658 device. For example, to support 10/100/1000 copper

SFPs, the MAC must be able to operate in SGMII mode. Because the MAC controls the establishment of

the link, PHY registers 0 through 15 and the PHY LEDs do not indicate link information when in SerDes

Pass-Through Mode. In this case, the only supported LED operation is the force on and force off modes.

A pass-through link is established when the SIGDET pin is asserted.

4.3

SGMII MAC-to-100BASE-FX Mode

The VSC8658 can support the 100BASE-FX communication speed to connect to fiber modules, such as

GBICs and SFPs.

This capability is facilitated by using the connections on the SerDes pins when connected to a MAC

through SGMII. Ethernet Package Generator (EPG), cyclical redundancy checking (CRC) counters, and

loopback modes are supported in the 100BASE-FX over SerDes mode. For information about how the

VSC8658 LEDs operate in this mode, see LED Behavior, page 19.

For information about how to configure the VSC8658 in 100BASE-FX mode using the twisted pair

interface, see 100BASE-FX Control, page 54.

4.4

Automatic Media-Sense (AMS) Interface Mode

This mode can automatically set the media interface to Cat5 or to SerDes interface modes automatically.

The active media mode chosen is based on the automatic media-sense (AMS) preferences set in the

device register 23, bit 11.

The following illustration shows a block diagram of the AMS functionality in the VSC8658 device.

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