TNETX4090 datasheet(41/78 Pages) TI1

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TNETX4090

ThunderSWITCH II™ 9-PORT 100-/1000-MBIT/S ETHERNET™ SWITCH

SPWS044E – DECEMBER 1997 – REVISED AUGUST 1999

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

ring-cascade topology (continued)

D Frames received on a ring port must have an out-of-band pretag in the clock cycle before Mxx_RXDV is

asserted. The contents of the pretag are examined, and based on the results, are either forwarded normally,

or immediately discarded within the MAC. If discarded, the frame does not affect any of the statistics or

address-lookup database. Frames are forwarded normally, unless:

–

The pretag is 0.

–

The two IDs within the pretag are not the same.

–

The ID within the received pretag is the same as ringid. This identifies a frame that originated at this

device, and that has passed completely around the ring.

The pretag format is shown in Figure 8.

Ring ID

Preamble

M08_TXD3–

M08_TXD0/

M08_RXD3–

M08_RXD0

M08_TXEN

M08_RXDV

M08_GTCLK

Ring ID

Preamble

M08_TXD7–

M08_TXD4/

M08_RXD7–

M08_RXD4

Figure 8. Ring-Topology Pretag Timing

The devices in the ring are connected as shown in Table 13.

Table 13. Ring-Topology Connectivity

SWITCH TERMINAL

n + 1

M08_TXD7

→

M08_RXD7

M08_TXD6

→

M08_RXD6

M08_TXD5

→

M08_RXD5

M08_TXD4

→

M08_RXD4

M08_TXD3

→

M08_RXD3

M08_TXD2

→

M08_RXD2

M08_TXD1

→

M08_RXD1

M08_TXD0

→

M08_RXD0

M08_TXEN

→

M08_RXDV

M08_TXER

→

M08_RXER

M08_COL

←

FLOW

NOTE: When a port is configured for the ring

topology, IEEE Std 802.3x flow control

should be disabled. Hardware-based

flow control is supported using the

FLOW

and

Mxx_COL

terminals;

however, this must be enabled by

setting the flow bit in SysControl.

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