TNETX15VE datasheet(63/113 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

PRINCIPLES OF OPERATION

determining the 2-bit VLANID for lookups and wire adds

The VLANID (used for lookup and wire-add operations) is the VLAN assigned to the source port. There are two

different ways to determine the VLANID for the source port, and the method used depends on the source port

number.

source port is 01 through 14

When the source port is 01–14, take the VLANID from the VLANID register for the source port [VLANDID

0x78–0x7F (DIO)].

source port is 00 (uplink)

If the frame comes from port 00, the tag field is used as an offset into the tagVLAN array [0x70–0x77 (DIO)].

The tagVLAN registers (16 total) support the four bits from the packet pretag field.

This offset method allows three possible cases:

• When two TNETX3150/TNETX3150As are connected through port 00 (current device is called

TNETX3150/TNETX3150A No. 1 and the remote TNETX3150/TNETX3150A No. 2), the tag coming

into TNETX3150/TNETX3150A No. 1 gives the source port for TNETX3150/TNETX3150A No. 2. If the

tagVLAN register array is filled with the VLANIDs for the ports in TNETX3150/TNETX3150A No. 2,

VLANs are transferred across port 00. This means that TNETX3150/TNETX3150A No. 1 tagVLAN

array mirrors the VLANIDs of TNETX3150/TNETX3150A No. 2 and vice versa.

• When TNETX3150/TNETX3150A is connected to a proprietary integrated circuit (IC) through port 00,

the third party IC uses the tag field to send across the VLANID of the frame. The TNETX15VE uses the

tag as the offset to the tagVLAN register array. If the tagVLAN register array is filled with its offset

number (see Table 3), the tag field corresponds to the VLANID.

• When port 00 is connected as an ordinary port (end equipment does not support pretagging), port 00’s

VLANID is put into all 16 locations of the tagVLAN register array. No matter what offset is latched during

the pretag time, the correct VLANID is used.

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