AM79C976 datasheet(78/309 Pages) AMD

78 / 309 page

Am79C976

8/01/00

P R E L I M INARY

VLAN Support

Virtual Bridged Local Area Network (VLAN) tags are

defined in IEEE Std 802.3ac-1998. A VLAN tag is a

4-byte quantity that is inserted between the Source

Address field and the Length/Type field of a basic 802.3

MAC frame. The VLAN tag consists of a Length/Type

field that contains the value 8100h and a 16-bit Tag

Control Information (TCI) field. The TCI field is further

divided into a 3-bit User Priority field, a 1-bit Canonical

Format Indicator (CFI), and a 12-bit VLAN Identifier.

A frame that has no VLAN tag is said to be untagged.

A frame with a VLAN tag whose VLAN Identifier field

contains the value 0 is said to be priority-tagged. A

frame with a VLAN tag with a non-zero VLAN Identifier

field is said to be VLAN-tagged.

The format of a VLAN-tagged frame is shown in

Figure 32.

XmtBackPressure

The total number of back pressure collisions

generated.

XmtFlowCtrl

PAUSEMACCtrlFramesTransmitted

The total number of PAUSE packets

generated and transmitted by the controller

hardware.

XmtPkts64Octets

RMON etherStatsPkts64Octets

The total number of packets (excluding error

packets) that are 64 bytes long.

XmtPkts65to127Octets

RMON etherStatsPkts65to127Octets