LAN9116 Datasheet, PDF (17/109 Pages) SMSC Corporation – Highly Efficient Single-Chip 10/100 Non-PCI Ethernet Controller

FIGURE 3-2:
VLAN FRAME
LAN9116
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.
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DS00002268A-page 17