LAN9420 Datasheet, PDF (61/171 Pages) SMSC Corporation – Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface

Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
DST
T
SRC
Y
P
E
Frame Data
F
C
S
Calculate Checksum
Figure 3.19 RXCOE Checksum Calculation
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:
DST
p
SRC
r
o
t
L3 Packet
F
C
S
0123
Calculate Checksum
Figure 3.20 Type II Ethernet Frame
DST
SRC
8
1
0
0
V
I
D
t
y
p
e
L3 Packet
F
C
S
01234
Calculate Checksum
Figure 3.21 Ethernet Frame with VLAN Tag
SMSC LAN9420/LAN9420i
61
DATASHEET
Revision 1.6 (07-18-11)