High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

both are set to the same value, VLAN1 is given higher precedence and the maximum legal frame length is set to 1522.

Standard Ethernet Frame (1518 Bytes)

Preamble

SOF

Dest. Addr.

Source Addr.

Type

Data

FCS

7 Bytes

1 Byte

6 Bytes

6 Bytes

2 Bytes

46-1500 Bytes

4 Bytes

Ethernet Frame with VLAN TAG (1522 Bytes)

Preamble

SOF

Dest. Addr.

Source Addr.

TPID

Type

Type

Data

FCS

7 Bytes

1 Byte

6 Bytes

6 Bytes

2 Bytes

2 Bytes

2 Bytes

46-1500 Bytes

4 Bytes

Tag Control Information

(TCI)

TPID

User Priority

CFI

 

VLAN ID

 

2 Bytes

3 Bits

1 Bit

 

12 Bits

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Defines the VLAN to

 

 

 

 

 

 

 

 

 

 

 

 

 

 

which the frame belongs

 

 

 

 

 

Canonical Address Format Indicator

 

 

 

 

 

Indicates the frame’s priority

Tag Protocol ID: \x81-00

Figure 9.1 VLAN Frame

9.4Address Filtering

The Ethernet address fields of an Ethernet packet consist of two 6-byte fields: one for the destination address and one for the source address. The first bit of the destination address signifies whether it is a physical address or a multicast address.

The Host MAC address check logic filters the frame based on the Ethernet receive filter mode that has been enabled. The various filter modes of the Host MAC are specified based on the state of the control bits in the Host MAC Control Register (HMAC_CR), as shown in Table 9.1. Please refer to the Section 14.3.1, "Host MAC Control Register (HMAC_CR)," on page 270 for more information on this register.

If the frame fails the filter, the Host MAC does not receive the packet. The host has the option of accepting or ignoring the packet.

Note: This filtering function is performed after any switch fabric filtering functions. The user must ensure the switch filtering is setup properly to allow packets to be passed to the Host MAC for further filtering.

Revision 1.4 (08-19-08)

114

SMSC LAN9312

 

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