TNETX15VE datasheet(21/113 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

internal register descriptions

revision register, revision at 0x00 (DIO)

MOST-SIGNIFICANT

BIT

LEAST-SIGNIFICANT

BIT

Product Code

Revision

Initial Values After Reset

This register contains the revision code for the device. The initial revision code is hardwired to 0x20, which

indicates the version 2.0 device. This register is read only, and writes to it are ignored.

SRAM size-select register, RAMsize at 0x01 (DIO)

The RAMsize register can be written to only when the START bit in the control register is set to 0. This register

is automatically loaded from the EEPROM when the RESET terminal is asserted low, when DIO address high

BIT

Reserved

RSIZE

Initial Values After Reset

BIT

NAME

FUNCTION

7–4

Reserved

Writes to this location are ignored and are read as 0.

3–0

RSIZE

Ram size select. This field indicates the size of the external SRAM, and has a bearing on the number of

addresses that the TNETX15VE supports. The TNETX15VE uses this field to determine how many tables

to initialize as part of the reset sequence by indicating how many address lines to use. All the intermediate

pointers used for address decode are stored in external SRAM, which means external SRAM is required.

The end points of an address lookup are stored in the internal RAM for speed. The internal SRAM is used

also for the one-address/port FIFO, and the 32-location FIFO used to record source addresses for frames

that override the receive block (spanning-tree BPDU support). This field is written only when the START bit

is 0. This field also is loaded from the EEPROM interface during auto-load.

Code values are as follows:

RAMsize

640

× 16

RAM

SIZE

WORST

CASE

0x00

832

× 16

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0x09

0x0A

0x0B

0x0C

0x0D to 0x0F

× 16

16K

× 16

32K

× 16

64K

× 16

128K

× 16

256K

× 16

512K

× 16

Reserved

123

251

507

1019

1954

Caution should be taken not to specify more RAM than is actually present. The state machines allocating

space treat this value literally. Unusual effects concerning addresses can be observed if this space is smaller

than indicated. For instance, addresses can appear more than once with the first few bits changed to 1s.

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