TNETX3150 datasheet(26/113 Pages) TI1

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TNETX3150/TNETX3150A

ThunderSWITCH™ 15-PORT 10-/100-MBIT/S ETHERNET™ SWITCH

SPWS027F – FEBRUARY 1997 – REVISED SEPTEMBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

cascade connection (continued)

Cascade employs the TNETX3150/TNETX3150A uplink connection of 200 Mbit/s. The necessity to provide

routing information with post tagging is disabled by option bit TAGOFF (bit 4) of DIO 0x00C2 RSIZE register.

The frame-control signal (M00TXER is asserted during FIFO underrun) is connected to M00RXDVX, permitting

the receiver to temporarily stall before continuing frame reception. This allows the TNETX3150/TNETX3150A

to reconstruct the frame. Flow control, implemented by holding M00COL high before frame transmission, is

retained to enable flow-controlled interfaces when required.

uplink frame RX routing via post tagging

If the TNETX3150/TNETX3150A relies on the external switch logic to make switching decisions (200-Mbit/s

mode and the TAGOFF option bit is reset), the external hardware must provide an indication of the destination

ports for the frame received on the uplink. This indication consists of four bytes. The EAM interface and the post

tag should not be used at the same time. When post tagging is enabled, the tag bytes overwrite the value

received on the EAM interface (EAM interface has no effect). When post tagging is turned off (designed for local

switching), the post tag is ignored, and the EAM interface or the internal address match supplies the routing

information.

There is no handshake or flow control for the receive uplink path on the TNETX3150/TNETX3150A. If required,

this must be implemented in upstream devices. No preamble is expected on data received by the uplink at

200-Mbit/s (see Figure 8). The tag fields are coded as shown in Figure 9.

M00RXD7–

M00RXD0

M00RXDVX

M00RCLK

M00RXDV

Tag 0

Tag 1

Tag 2

Tag 3

Don’t Care

DA, SA, Data, CRC,

Ethernet Frame

Idle Cycle

(at least 1 cycle)

4-Byte Tag Field Appended

to the End of the Ethernet

Frame Reception

Figure 8. Data Format for Uplink RX Frames

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