TNETX15AE datasheet(57/78 Pages) TI

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TNETX15AE

ADDRESS-LOOKUP DEVICE

SPWS041A – AUGUST 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

NAUTO mode

NAUTO mode is selected by asserting the NAUTO bit in the control register. In NAUTO mode, the ADD logic

operation does not add addresses off the wire. The only way addresses are added, moved, or edited is through

the register interface. The host processor is assumed to have complete control of the contents of the

address table.

NLRN0 mode

The ADD logic operation cannot add addresses learned from port 0 when this bit is set. The bus watcher does

not extract these addresses from the DRAM bus. In this mode, the management CPU can add an address for

port 0 (the hardware does not). Since the bus watcher does not provide addresses from these ports to ADD in

this mode, ADD does not perform any age process on any addresses in the lookup table assigned to port 0 in

this mode; nor, are the NEW, CHNG, or SECVIO interrupts active for port 0 in this mode.

NCRC mode

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

the source address is given to ADD. The TNETX15AE performs additions faster in NCRC mode since it does

not have to wait for the good CRC indication on the bus. If the TNETX15AE is waiting for a good CRC, after a

bad packet on a seldom-used port, no addresses are being added on any port, although, lookup is functioning

normally for destination addresses already in the table. If this bit is set, there is a possibility that addresses from

bad (bad or missing CRC) frames are added, but the aging process deletes them eventually.

management address adding

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

address interface registers as shown in the following:

BYTE 3

BYTE 2

BYTE 1

BYTE 0

DIO

ADDRESS

Adddelcontrol

0x2C

Addnode23–Addnode16

Addnode31–Addnode24

Addnode39–Addnode32

Addnode47–Addnode40

0x38

Addport

Addnode7–Addnode0

Addnode15–Addnode8

0x3C

Management ADDs are used to perform the following functions:

D The address flags SECURE, LOCKED, and the copy uplink flag, CUPLINK, can be set or cleared through

management adds.

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

D DIO ADDs also are the only way multicast addresses are added to the lookup table.

D 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:

D Write the node’s address in the addnode registers.

D 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.

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

TNETX15AE 数据表(PDF) 57 Page - Texas Instruments

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