8101 datasheet(36/172 Pages) LSI

36 / 172 page

2-18

Functional Description

2.8.3 Unicast Address Filter

Comparing the destination address of the receive packet against the

48-bit value stored in the three MAC Address registers (registers 0, 1

and 2) ﬁlters unicast packets. When the destination address of a unicast

packet matches the value stored in these registers the unicast packet is

deemed valid and passed to the receive FIFO; otherwise, the packet is

rejected. The correspondence between the bits in the MAC Address

registers and the incoming bits in the destination address of the receive

packet is deﬁned in the MAC Address register deﬁnitions.

To program the controller to always reject unicast packets, set the

REJUCST bit in “Register 8–Conﬁguration 2‚" Section 4.3.9. When this

bit is set all unicast packets are rejected regardless of their address.

Unicast packet address ﬁltering functions do not affect the reception of

MAC control frames. Other bits described in Section 2.17, “MAC Control

Frames,” control the reception of MAC control frames.

2.8.4 Multicast Address Filter

The multicast address ﬁlter function computes the CRC on the incoming

Destination Address and produces a 6-bit number that is compared

against the 64 values stored in the MAC Address Filter 1

−4 registers

(Registers 3, 4, 5, and 6). When the multicast packet destination address

passes the address ﬁlter, the packet is deemed valid and passed to the

receive FIFO; otherwise, the packet is rejected.

The multicast address ﬁlter requires 64 address ﬁlter bits to be written

into the Address Filter 1

−4 registers. The multicast address ﬁltering

algorithm is as follows:

Compute a separate 32-bit CRC on the destination address ﬁeld

using the same IEEE 802.3 deﬁned method that computes the

transmit CRC.

Use bits [0:2] of the destination address FCS to select one of the

bytes in the 64-bit address ﬁlter, as shown in Table 2.5.

Use bits [3:5] of the destination address FCS to select one of the bits

within the byte selected in (2), as shown in Table 2.5.

8101 Datasheet(PDF) 36 Page - LSI Computer Systems