TNETX15AE datasheet(54/78 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

lookup table SRAM initialization (START)

The lookup table is automatically initialized by the TNETX15AE, with no need for an external processor. The

steps for initializing are:

D Write to RAMsize the size of the external SRAM. Writing to RAMsize can be performed by a CPU before

START is set or via the EEPROM auto-load operation.

D Assert the START bit in the control register. This is accomplished either by the CPU or EEPROM.

D The TNETX15AE indicates the completion of the lookup-table initialization by setting the INITD bit in the

control register to 1.

The TNETX15AE clears the lookup table by writing 0x0000 to all available locations and then initializes the

memory data structures. After these operations are done, the TNETX15AE performs lookups, adding, and aging

operations as directed by mode bits.

frame-forwarding LKUP logic operation

The lookup (LKUP) logic operation is designed for two important tasks: 1) perform time-critical lookups of the

wire within the TNETX3150/TNETX3150A/TNETX3100’s allotted time, and 2) forward the frame to the right

ports. The LKUP logic operation works independently of all other logic operations. To meet the timing

requirements, this logic operation occupies the highest priority on the SRAM bus after SRAM is initialized for

looking up destination addresses. LKUP performs a lookup on the destination address found from the DRAM

interface.

If an address is found, the TNETX15AE uses the information contained in the lookup table for routing. If the

address is not found, the TNETX15AE floods the frame to the ports indicated in the unkmultiports or unkuniports

management-based lookups (FIND)

The LKUP logic operation also is called when the DIO interface sets the FIND (LKUP) bit in the findcontrol

the lookup table. FIND is controlled from the following internal registers:

BYTE 3

BYTE 2

BYTE 1

BYTE 0

DIO

ADDRESS

Findnode23–Findnode16

Findnode31–Findnode24

Findnode39–Findnode32

Findnode47–Findnode40

0x0C

Findport

Findnode7–Findnode0

Findnode15–Findnode8

0x10

Findcontrol

Findnodeage

0x14

The interface provides a 48-bit read or writeable register findnode in which the address is placed; a 16-bit

age time stamp of the node being looked up.

TNETX15AE 数据表(PDF) 54 Page - Texas Instruments

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