TNETX15VE datasheet(51/113 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

TNETX15VE DRAM and EAM interface

The TNETX15VE takes its frame input through the TNETX3150/TNETX3150A DRAM bus. It must recognize

a start-of-frame indication (SOF) on the first flag byte of the frame. After the SOF is found, the TNETX15VE

latches the first 32 bits of the destination address on the next DRAM cycle. From this time, it must complete a

lookup cycle, decide on the appropriate EAM code, and output this code in 440 ns, or less. Figure 2 shows the

lookup timing. Check the data set for the TNETX3150/TNETX3150A for field definitions beyond those used by

the TNETX15VE.

OSCIN

DOE

DWE

DRAS

DCAS

Row

Col

FPTR

Data

Col

Data

0PPP

01UU CCCC

00UU

1BBB

1SSS

CCCC

00UU

CCCC

00UU

DA7–DA0

DX2–DX0

DD31–

DD0

DD35–

DD32

EAM15–

EAM0

Forward Pointer Field

(Request Port Code)

High Nibble of

Start Flag (SOF)

Most-Significant 32 Bits of

Destination Address (DA) Latched

(Decode May Begin)

End-of-Buffer

(EOB)

External Address Match

(EAM) Code Valid

End-of-Flag

(EOF)

440 ns

0 ns

250 ns

500 ns

750 ns

Cycle

Figure 2. Lookup Cycle Timing

The data on each cycle has the following format. The TNETX15VE must determine that the data being written

to memory is the first buffer of a data frame and not an IOB index buffer. The buffer contains packet data if the

IOB bit is 0. The port number and VLAN assignment for the frame is latched from the channel code. The channel

code is the source port.

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