LAN9500 Datasheet, PDF (64/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

LAN950x
FIGURE 5-10:
RXCOE CHECKSUM CALCULATION
DST
T
SRC
Y
P
E
Frame Data
F
C
S
Calculate Checksum
In mode 1, the RXCOE supports VLAN tags and a SNAP header. In this mode, the RXCOE calculates the checksum at
the start of L3 packet. The VLAN1 tag register is used by the RXCOE to indicate what protocol type is to be used to
indicate the existence of a VLAN tag. This value is typically 8100h.
Example frame configurations:
FIGURE 5-11:
TYPE II ETHERNET FRAME
p
DST
SRC
r
o
t
L3 Packet
F
C
S
0123
1DWORD
Calculate Checksum
FIGURE 5-12:
ETHERNET FRAME WITH VLAN TAG
DST
SRC
8
1
0
0
V
I
D
t
y
p
e
L3 Packet
F
C
S
01234
1DWORD
Calculate Checksum
DS00001875A-page 64
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