![](http://datasheet.mmic.net.cn/380000/-PD98405_datasheet_16745025/-PD98405_208.png)
CHAPTER 5 SAR FUNCTION
208
(3) Discarding a receive packet by LECID matching
The
μ
PD98405 can automatically discard a receive packet if it has the same LECID as its own LECID. The
μ
PD98405's LECID, which will be compared with a receive LECID, can be set in the LOCAL LECID field of
the receive VC table for each VC. This enables connection to more than one emulated LAN. If the LFE bit
of the receive VC table is set to 1, the
μ
PD98405 compares the value in the LOCAL LECID field of a
receive VC table with the receive LECID of the relevant VC. If they match, the
μ
PD98405 discards all the
cells, up to the last one, that belong to this receive packet.
(4) Receive packet filtering based on MAC address matching
The
μ
PD98405 supports receive packet filtering based on MAC address (destination address) matching.
Whether to enable or disable filtering can be selected separately for individual VCs. If the DAF bit of a
receive VC table is set to 1, filtering is enabled for the VC table. The host sets the destination address to
be submitted to filtering reception in the MAU, MAL, HTU, and HTL registers. The position of the
destination address within the receive packet is variable. This configuration enables the support of frame
formats such as the Ethernet and token-ring frame formats. The host loads the MAC field of a receive VC
table with the byte position of the destination address relative to the beginning of the receive packet. The
μ
PD98405 identifies the destination address according to the value in the MAC field, as listed below:
MAC field value
Byte position relative to the
beginning of the receive packet
"00"
2 bytes (Ethernet)
"01"
4 bytes (Token-Ring)
"10"
6 bytes
"11"
10 bytes
The size of the destination address used in filtering is fixed to 6 bytes.
The
μ
PD98405 checks the destination address in the receive packet, and determines whether to accept or
discard the receive packet. Filtering is executed by means of the following three steps: