TNETX15VE datasheet(45/113 Pages) TI1

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TNETX15VE

VLAN-ENGINE ADDRESS-LOOKUP DEVICE

SPWS028B – APRIL 1997 – REVISED SEPTEMBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

port 00 tag VLAN array, tagVLAN at 0x70–0x77 (DIO)

BYTE 3

BYTE 2

BYTE 1

BYTE 0

DIO ADDRESS

TagVLAN6/TagVLAN7

TagVLAN4/TagVLAN5

TagVLAN2/TagVLAN3

TagVLAN0/TagVLAN1

0x70

TagVLAN14/TagVLAN15

TagVLAN12/TagVLAN13

TagVLAN10/TagVLAN11

TagVLAN8/TagVLAN9

0x74

The format for the tagVLAN register is (x/y):

BIT

Reserved

VLANID – Offset x

Reserved

VLANID – Offset y

Initial Values After Reset

The tagVLAN register array is used with the tag field in the forward pointer portion of the DRAM interface to

chose the VLANID. This array is only valid when a frame comes in from port 00 (uplink).

Each byte contains two VLANIDs, one for each offset (x/y) specified in the name. All VLAN IDs default to 0x0

on a reset. These registers are automatically loaded from the EEPROM in a hardware reset (RESET = 0 or when

DIO address high is 0x40) or when the LOAD bit in the control register is set.

VLANIDs can be interpreted in several ways. In a cascaded situation, the VLANID is a copy of the pretag that

the other system put in front of the packet, and it is used to get the VLANID of the source port for the packet

as it entered the remote system. The value that is prepended to the packet is used as an index to this table to

retrieve the VLANID. In this case, VLANID15 is not likely to be used because the TNETX3150/TNETX3150A

cannot have a packet sourced from a port that does not exist.

If this system is connected to a larger system, then the value prepended to the packet is an external indication

of the VLAN for the incoming packet. Functioning as a pointer to this table, any value in the 4-bit field is allowed.

The TNETX15VE device only supports four VLANIDs in this array (two least-significant bits of a 4-bit field), and

any value in the pretag field can be used to index to the table. For this reason it is important to fill in all the values

in the table unless the higher entity can be restricted to four values of the pretag for four supported VLANIDs.

Future versions of the address-lookup engine might support all four bits or 16 VLANs.

If port 00 is connected to an entity that does not control the pretag field, VLANs cannot extend out of this

TNETX3150/TNETX3150A and TNETX15VE combination. If the packet comes from port 00, the value clocked

off the wire is used as an index to this table. All the table entries must represent the VLANID assigned to port

00 because any value can be clocked off the wire.

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