Non-PCI Single-Chip Full Duplex Ethernet Controller
Chapter 6 Packet Format in Buffer memory for
Ethernet
The packet 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 packet memory format is word oriented.
bit0
bit15
2nd Byte
RAM
OFFSET
1st Byte
(DECIMAL)
0
STATUS WORD
2
4
BYTE COUNT (always even)
RESERVED
DATA AREA
1534 Max
LAST DATA BYTE (if odd)
CONTROL BYTE
Last Byte
Figure 6.1 – Data Packet Format
TRANSMIT PACKET
Written by CSMA upon transmit Written by CSMA upon receive
completion (see Status Register) completion (see RX Frame
Status Word)
RECEIVE PACKET
STATUS WORD
BYTE COUNT
DATA AREA
CONTROL BYTE
Written by CPU
Written/modified by CPU
Written by CSMA
Written by CSMA
Written by CPU to control
Written by CSMA. Also has
ODD/EVEN data bytes
ODD/EVEN bit
Rev. 11/18/2004
Page 30
SMSC DS – LAN91C96I
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