CS8900A
Crystal LAN™ ISA Ethernet Controller
memory by DMA). The DA filter can be config- 5.3.1 Configuring the Destination Address Filter
ured to accept the following frame types:
The DA filter is configured by programming five
DA filter bits in the RxCTL register (Register 5):
IAHashA, PromiscuousA, MulticastA, Individua-
lA, and BroadcastA. Four of these bits are associat-
ed with four status bits in the RxEvent register
(Register 4): IAHash, Hashed, IndividualAdr, and
Broadcast. The RxEvent register reports the results
of the DA filter for a given receive frame. The bits
associated with DA filtering are summarized be-
low:
5.3.0.1 Individual Address Frames
For all Individual Address frames, the first bit of
the DA is a "0" (DA[0] = 0), indicating that the ad-
dress is a Physical Address. The address filter ac-
cepts Individual Address frames whose DA
matches the Individual Address (IA) stored at
PacketPage base + 0158h, or whose hash-filtered
DA matches one of the bits programmed into the
Logical Address Filter (the hash filter is described
later in this section).
Bit #
RxCTL
RxEvent
Register 5
Register 4
5.3.0.2 Multicast Frames
6
IAHashA
IAHash
(used only if IAHashA = 1)
For Multicast Frames, the first bit of the DA is a "1"
(DA[0] = 1), indicating that the frame is a Logical
Address. The address filter accepts Multicast
frames whose hash-filtered DA matches one of the
bits programmed into the Logical Address Filter
(the hash filter is described later is this section). As
shown in Table 25, Broadcast Frames can be ac-
cepted as Multicast frames under a very specific set
of conditions.
7
9
PromiscuousA
MulticastA
Hashed
A
IndividualA
IndividualAdr
(used only if IndividualA = 1)
B
BroadcastA
Broadcast
(used only if BroadcastA = 1)
The IAHashA, MulticastA, IndividualA, and
BroadcastA bits are used independently. As a re-
sult, many DA filter combinations are possible. For
example, if MulticastA and IndividualA are set,
then all frames that are either Multicast or Individ-
ual Address frames are accepted. The Promiscu-
ousA bit, when set, overrides the other four DA
bits, and allows all valid frames to be accepted. Ta-
ble 24 summarizes the configuration options avail-
able for DA filtering.
5.3.0.3 Broadcast Frames
Frames with DA equal to FFFF FFFF FFFFh are
broadcast frames. In addition, the CS8900A can be
configured for Promiscuous Mode, in which case it
will accept all receive frames, irrespective of DA.
IAHashA
PromiscuousA MulticastA IndividualA
BroadcastA
Frames Accepted
0
0
0
0
0
0
1
1
0
0
0
Individual Address frames with
DA matching the IA at Pack-
etPage base + 0158h
1
0
Individual Address frames with
DA that pass the hash filter
(DA[0] must be “0”)
0
0
Multicast frames with DA that
pass the hash filter (DA[0] must
be “1”)
0
0
1
0
0
1
Broadcast frames
All frames
X
X
X
X
Table 24. DA Filtering Options
CIRRUS LOGIC PRODUCT DATA SHEET
88
DS271PP3
CIRRUS [ CIRRUS LOGIC ]
