EMAC Registers
956
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Ethernet Controller
15.6.8 EMACVLANTG Register (Offset = 0x1C) [reset = 0x0]
Ethernet MAC VLAN Tag (EMACVLANTG)
The Ethernet MAC VLAN Tag (MACVLANTG) register contains the IEEE 802.1Q VLAN Tag to identify the
VLAN frames. The MAC compares the 13th and 14th bytes of the receiving frame (Length/Type) with the
value 0x8100, and the following two bytes are compared with the VLAN tag. If a match occurs, the MAC
sets the received VLAN bit in the receive frame status. The legal length of the frame is increased from
1518 bytes to 1522 bytes.
EMACVLANTG is shown in
and described in
Return to
Figure 15-23. EMACVLANTG Register
31
30
29
28
27
26
25
24
RESERVED
R-0x0
23
22
21
20
19
18
17
16
RESERVED
VTHM
ESVL
VTIM
ETV
R-0x0
R/W-0x0
R/W-0x0
R/W-0x0
R/W-0x0
15
14
13
12
11
10
9
8
VL
R/W-0x0
7
6
5
4
3
2
1
0
VL
R/W-0x0
Table 15-32. EMACVLANTG Register Field Descriptions
Bit
Field
Type
Reset
Description
31-20
RESERVED
R
0x0
19
VTHM
R/W
0x0
VLAN Tag Hash Table Match Enable.
0x0 = The VLAN Hash Match operation is not performed.
0x1 = The most significant four bits of the VLAN tag's CRC are used
to index the content of the MAC VLAN Hash Table
(EMACVLANHASH) register. A value of 1 in the EMACVLANHASH
register, corresponding to the index, indicates that the frame
matched the VLAN hash table.When Bit 16 (ETV) is set, the CRC of
the 12-bit VLAN Identifier (VID) is used for comparison whereas
when ETV is reset, the CRC of the 16-bit VLAN tag is used for
comparison.
18
ESVL
R/W
0x0
Enable S-VLAN.
0x0 = The MAC transmitter does not recognize S-VLAN frames as
valid VLAN tagged frames.
0x1 = The MAC transmitter and receiver considers the S-VLAN
(Type = 0x88A8) frames as valid VLAN tagged frames.
17
VTIM
R/W
0x0
VLAN Tag Inverse Match Enable.
0x0 = VLAN perfect matching is enabled. The frames with matched
VLAN tag are marked as matched.
0x1 = VLAN tag inverse matching is enabled. The frames that do not
have matching VLAN tag are marked as matched.
16
ETV
R/W
0x0
Enable 12-Bit VLAN Tag Comparison.
0x0 = All 16 bits of the 15th and 16th bytes of the received VLAN
frame are used for comparison and VLAN hash filtering.
0x1 = A 12-bit VLAN identifier is used for comparing and filtering
instead of the complete 16-bit VLAN tag.Bits [11:0] of VLAN tag are
compared with the corresponding field in the received VLAN-tagged
frame. Similarly, when enabled, only 12 bits of the VLAN tag in the
received frame are used for hash-based VLAN filtering.