TNETX15VE datasheet(52/113 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 (continued)

The TNETX15VE must determine the start of frame by looking at the flag in cycle 1. The flag is given in the

DD35–DD32 terminals. The SOF is shown in the following table in cycle 1 at bit (35–34) = 01b.

CYCLE

BIT

IOB

Parity

Tag

Channel code

Forward pointer†

Reserved

Most-significant 32 bits of destination address (DA)

Channel code

Most-significant 16 bits of source address (SA)

Least-significant

16 bits of DA

Reserved

Least-significant 32 bits of SA

Flags

Data

N–1

EOB

Valid bytes

Data

EOF

Frame status

CRC

† These bits are ignored by the TNETX15VE.

The TNETX15VE cycle begins when it latches the partial destination address to begin the table lookup, and

ends when it outputs an EAM code within the allocated 440 ns after the SOF condition is met.

The channel-code field in the flags of the body of the frame is exactly the same as that in the forward pointer.

The TNETX15VE uses the channel code from the forward pointer.

tag field

The tag field in the forward pointer comes from the port 00 pretag; that is, this field is defined only if the packet

source port is 00. Figure 3 shows the tag in relation to the rest of the frame. Please consult the latest

TNETX3150/TNETX3150A documentation for additional information.

M00RCLK

M00RXD7–

M00RXD0

Don’t Care

Tag

DA, SA, Data, CRC

M00RXDV

Don’t Care

1-Byte Tag Field Added to the Frame

Note at 200 Mbit/s, No Preamble is Transmitted.

Figure 3. Field Format for Uplink-Port Receive (RX) Frames

The pretag byte format is as follows:

BIT

Reserved

Source port number

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