LAN9117_08 Datasheet, PDF (26/136 Pages) SMSC Corporation – High Performance Single-Chip 10/100 Non-PCI Ethernet Controller

High Performance Single-Chip 10/100 Non-PCI Ethernet Controller
Datasheet
Figure 3.2 VLAN Frame
The MAC Function recognizes transmitted and received frames tagged with either one-level or two-
level VLAN IDs. The MAC compares the thirteenth and fourteenth bytes of transmit and receive frames
to the contents of both the one-level VLAN tag register and the two-level VLAN tag register. If a match
is found, the MAC Function identifies the frame as either a one- or two-level VLAN frame, depending
on where the match was found. Upon recognizing that a frame has a VLAN tag, counter thresholds
are adjusted to account for the extra bytes that the VLAN tag adds to the frame. The maximum length
of the good packet is thus changed from 1518 bytes to 1522 bytes.
Revision 1.5 (07-11-08)
26
DATASHEET
SMSC LAN9117