IP178C/IP178C LF/IP178CH/IP178CH LF
Datasheet
36/93
June 21, 2007
Copyright © 2004, IC Plus Corp.
IP178Cx-DS-R12
2.5
Tag VLAN/ Tag and un-tag function
Tag and un-tag function
IP178C/IP178CH inserts or removes a tag of a frame if tagging/ un-tagging function is enabled. The
operation is illustrated as follows. The tag information is defined in MII register 30.3~30.11 and EEPROM
register 6~22.
The operation of a port which forwards the packet
Frame type of the
received packet
Forward to a untagged filed
Forward to a tagged field
Untagged
Forward
the
packet
without
modification
Insert a tag using the default VLAN tag
value of the source port
Calculate new CRC
The default VLAN tag value is defined in
the MII register 30.3~30.11.
Priority-tagged
(VLAN ID=0)
Strip tag
Calculate new CRC
Keep priority field.
Replace the tag with the default VLAN tag
value of the source port
Calculate new CRC
The default VLAN tag value is defined in
the MII register 30.3~30.11.
VLAN-tagged
Strip tag
Calculate new CRC
Forward the packet without modification
2.6
Tag VLAN
If tag VLAN function is enabled (MII register 30.13[3] TAG_VLAN_EN is logic high), IP178C/IP178CH
forwards a packet according to MAC address table and one of the sixteen VLAN output port masks,
defined in MII register 30.14~30.29. One of the sixteen VLAN output mask is selected by VID index,
which is four bits selected from VID field in a tag. VID index is defined in MII register 30.13[2:0] VID_SEL.
For example, VLAN output port mask 1 is selected if VID index selected by VID_SEL is equal to 1.
IP178C/IP178CH handles an un-tagged packet using the default VLAN tag value of its source port. A
packet with VID equal to 12’b0 will be handled as un-tag frame.
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