Datasheet

KSZ8795CLX
DS00002112B-page 82  2016-2017 Microchip Technology Inc.
Read Register 117 (31:24)
Read Register 118 (23:16)
Read Register 119 (15:8)
Read Register 120 (7:0)
2. Static Address Table Write (write the 8th entry)
Write Register 113 (62:56)
Write Register 114 (55:48)
Write Register 115 (47:40)
Write Register 116 (39:32)
Write Register 117 (31:24)
Write Register 118 (23:16)
Write Register 119 (15:8)
Write Register 120 (7:0)
Write to Register 110 with 0x00 (write static table selected)
Write to Register 111 with 0x7 (trigger the write operation)
4.5 VLAN Table
The VLAN table is used for VLAN table look-up. If 802.1q VLAN mode is enabled (Register 5 Bit[7] = 1), this table is
used to retrieve VLAN information that is associated with the ingress packet. There are three fields for FID (filter ID),
Valid, and VLAN membership in the VLAN table. The three fields must be initialized before the table is used. There is
no VID field because 4096 VIDs are used as a dedicated memory address index into a 1024x52-bit memory space.
Each entry has four VLANs. Each VLAN has 13 bits. Four VLANs need 52 bits. There are a total of 1024 entries to sup-
port a total of 4096 VLAN IDs by using dedicated memory address and data bits. FID has 7 bits to support 128 active
VLANs.
If 802.1q VLAN mode is enabled, the KSZ8795CLX assigns a VID to every ingress packet when the packet is untagged
or tagged with a null VID, the packet is assigned with the default Port VID of the ingress port. If the packet is tagged with
non-null VID, the VID in the tag is used. The look-up process starts from the VLAN table look-up based on VID number
with its dedicated memory address and data bits. If the entry is not valid in the VLAN table, the packet is dropped and
no address learning occurs. If the entry is valid, the FID is retrieved. The FID+DA and FID+SA lookups in MAC tables
are performed. The FID+DA look-up determines the forwarding ports. If FID+DA fails for look-up in the MAC table, the
packet is broadcast to all the members or specified members (excluding the ingress port) based on the VLAN table. If
FID+SA fails, the FID+SA is learned. To communicate between different active VLANs, set the same FID; otherwise set
a different FID.
TABLE 4-17: VLAN TABLE
Address Name Description Mode Initial Suggested Value
Format of Static VLAN Table (Support Max 4096 VLAN ID entries and 128 Active VLANs)
12 Valid 1 = The entry is valid.
0 = Entry is invalid.
R/W 0
11 - 7 Membership Specifies which ports are members of the
VLAN.
If a DA look-up fails (no match in both
static and dynamic tables), the packet
associated with this VLAN will be for-
warded to ports specified in this field.
E.g., 11001 means Ports 5, 4, and 1 are in
this VLAN.
R/W 111111
6 - 0 FID Filter ID. The KSZ8795CLX supports 128
active VLANs represented by these seven
bit fields. FID is the mapped ID. If 802.1q
VLAN is enabled, the look-up will be
based on FID+DA and FID+SA.
R/w 0