TNETX3150 datasheet(34/113 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

DRAM and EAM interfaces (continued)

flag bytes

Flag attributes are assigned to the deserialized data word, identifying key attributes. The flags are used in later

data handling. The flag field is assigned to every eight data bytes. The format of the subfields within the flag

byte changes, depending on the flag information. The formats shown in Figure 13 are the end-of-buffer and the

end-of-frame flag formats. When the most-significant bit (end-of-buffer bit) is set, the remaining bits of the

most-significant nibble contain the number of bytes in the data word, while the least-significant nibble contains

error/status information.

End of Buffer

Start of Frame

Unassigned

Broadcast /Multicast

Requesting Channel

Address Code /

Source Port Number

Don’t care

End-of-Buffer Bit

b) END-OF-BUFFER (EOB) FLAG BYTE FORMAT

End-of-Buffer Bit

c) END-OF-FRAME (EOF) FLAG BYTE FORMAT

Number of valid bytes in the data word

001 = 1, 010 = 2 . . . 111 = 7, 000 = 8

Data Word Error/Status

Good EOF

CRC Error

CV Error

OVF Error

Jabber Error

000

001

010

011

100

NOTE A: The EOB bit is asserted after each 64-byte data transfer. Only at the EOF is bit 3 of the flag byte set.

a) START-OF-FRAME (SOF) FORMAT

— No errors

— Bad CRC

— Code violation = alignment + bad CRC

— Overflow error = no buffers available

— Frame exceeds 1531 bytes

Figure 13. EOB, EOF, and SOF Flag Formats

TNETX3150 Datasheet(PDF) 34 Page - Texas Instruments

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