TNETX15AE datasheet(35/78 Pages) TI

35 / 78 page

TNETX15AE

ADDRESS-LOOKUP DEVICE

SPWS041A – AUGUST 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

EAM codings and in-order broadcasts (IOB) (continued)

The TNETX15AE uses single-port codings when possible, to maximize performance. The TNETX15AE

inspects all multiple-port codings. If, after removing all ineligible receivers (e.g., source port) only one

destination port is left, the TNETX15AE switches to a single-port coding on the EAM bus.

For a more complete description of IOB lists, refer to the latest TNETX3150/TNETX3150A/TNETX3100

specification.

TNETX15AE DRAM and EAM interface

The TNETX15AE takes its frame input through the TNETX3150/TNETX3150A DRAM bus. It must recognize

a start-of-frame (SOF) indication on the first flag byte of the frame. After the SOF is found, the TNETX15AE

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

lookup cycle, choose the appropriate EAM code, and output this code in 440 ns, or less. Figure 3 shows the

lookup timing. Check the data set for the TNETX3150/TNETX3150A/TNETX3100 for field definitions beyond

those used by the TNETX15AE. The data on each cycle has the following format.

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 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

Low

Least-Significant 16 Bits

of DA Latched

Figure 3. Lookup Cycle Timing

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