TNETX3100PGC datasheet(20/80 Pages) TI1

20 / 80 page

TNETX3100

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

SPWS031D – JUNE 1997 – REVISED OCTOBER 1997

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

flag byte

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

change, depending on the flag information. Previously, the start-of-frame format was described in the address

compare text (see Figure 7). The formats shown in Figure 7 are the end-of-buffer and the end-of-frame flag for-

mats. 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. Bit 3 of the flag byte is set only at the EOF.

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 7. EOB, EOF, and SOF Flag Formats

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