LAN91C96-MS datasheet(37/125 Pages) SMSC

37 / 125 page

Non-PCI Single-Chip Full Duplex Ethernet Controller with Magic Packet

SMSC LAN91C965v&3v

Page 37

Rev. 03-28-07

DATASHEET

Chapter 6

Frame Format in Buffer Memory for

Ethernet

The frame format in memory is similar to that in the TRANSMIT and RECEIVE areas. The first word is

reserved for the status word, the next word is used to specify the total number of bytes, and that in turn is

followed by the data area. The data area holds the packet itself, and its length is determined by the byte

count. The frame memory format is word oriented.

Figure 6.1 – Data Frame Format

TRANSMIT PACKET

RECEIVE PACKET

STATUS WORD

Written by CSMA upon transmit

completion (see Status Register)

Written by CSMA upon receive

completion (see RX Frame

Status Word)

BYTE COUNT

Written by CPU

Written by CSMA

DATA AREA

Written/modified by CPU

Written by CSMA

CONTROL BYTE

Written by CPU to control

ODD/EVEN data bytes

Written by CSMA. Also has

ODD/EVEN bit

BYTE COUNT - Divided by two, it defines the total number of words, including the STATUS WORD, the

BYTE COUNT WORD, the DATA AREA and the CONTROL BYTE.

The receive byte count always

appears as even, the ODDFRM bit of the receive status word indicates if the low byte of the last word is

RESERVED

BYTE COUNT (always even)

STATUS WORD

DATA AREA

LAST DATA BYTE (if odd)

bit0

bit15

RAM

OFFSET

(DECIMAL)

1534 Max

CONTROL BYTE

Last Byte

1st Byte

2nd Byte

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