TNETX15VE datasheet(85/113 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

NLRN mode

The ADD logic operation cannot generate any indication of a new address from ports whose learning has been

disabled by having its bit in the NLRNport register set. The bus watcher does not extract these addresses from

the DRAM bus so no table search is possible. In this mode, the management CPU can add an address on the

learning disabled ports. Since the bus watcher does not provide addresses from these ports to ADD in this mode,

ADD does not perform any age touches to any addresses in the lookup table assigned to ports in this mode.

NCRC mode

The NCRC bit controls whether or not the bus watcher waits for a complete valid (CRC checked) frame before

giving it to ADD. The TNETX15VE performs additions faster in NCRC mode since it does not have to wait for

the good CRC indication on the bus. There is a possibility that addresses from bad (CRC checked) frames are

added, but the aging process deletes them eventually.

management address adding

The ADD logic operation also can add addresses through the DIO interface management add/edit address

interface registers as shown in the following:

DIO ADDRESS

0x2C

BYTE 3

BYTE 2

BYTE 1

BYTE 0

0x38

0x3C

AddVLANID

Addnode7–Addnode0

Adddelcontrol

Addnode23–Addnode16

Addnode31–Addnode24

Addnode39–Addnode32

Addnode47–Addnode40

Addport

Addnode15–Addnode8

Management ADDs are used to perform the following functions:

• The address’ flags NEW, NBLCK, SECURE, LOCKED, and the copy uplink flag, CUPLINK, can be set

or cleared through management adds.

• DIO ADDs are used to change the address port assignment.

• DIO ADDs are also the only way multicast and broadcast addresses are added to the lookup table.

• DIO ADDs also write the current time to the AGE time stamp for the node.

Management add commands are given through the ADD bit in the adddelcontrol register. The steps for adding

an address are as follows:

• Write the node’s address in the addnode registers and its VLAN in addVLANID.

• If it is a unicast address, write the node’s flag information and port assignment in addport. If it is a

multicast address, write the forwarding mask.

• Set the ADD bit in the adddelcontrol register to 1.

The ADD logic operation locks the addnode, addVLANID, and addport registers to ensure that they do not

change during the address ADD. Reads to these registers are still possible. The ADD bit in the adddelcontrol

Having a sticky bit (remains a 1) for ADD gives the programmer the opportunity to setup or perform other register

operations without having to wait for the ADD completion. A polling method is used to find out if the ADD is

finished. This involves reading the adddelcontrol register to determine if the ADD bit is low. The command bit

stays set to 1 until command execution is completed.

TNETX15VE 数据表(PDF) 85 Page - Texas Instruments

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