
AMD
P R E L I M I N A R Y
170
Am79C965
18219B-44
47
1
0
RECEIVED MESSAGE
DESTINATION ADDRESS
1
CRC
GEN
SEL
31
26
0
MUX
MATCH
PACKET ACCEPTED
PACKET REJECTED
63
0
6
64
LOGICAL
ADDRESS
FILTER
(LADRF)
32-BIT RESULTANT CRC
MATCH
MATCH=1:
PACKET ACCEPTED
MATCH=0:
PACKET REJECTED
Figure 38. Address Match Logic
The Logical Address Filter is used in multicast address-
ing schemes. The acceptance of the incoming frame
based on the filter value indicates that the message may
be intended for the node. It is the node’s responsibility to
determine if the message is actually intended for the
node by comparing the destination address of the stored
message with a list of acceptable logical addresses.
If the Logical Address Filter is loaded with all zeroes and
promiscuous mode is disabled, all incoming logical ad-
dresses except broadcast will be rejected.
The Broadcast address, which is all ones, does not go
through the Logical Address Filter and is handled as
follows:
s If the Disable Broadcast Bit is cleared, the broadcast
address is accepted
s If the Disable Broadcast Bit is set and promiscuous
mode is enabled, the broadcast address is accepted.
s If the Disable Broadcast Bit is set and promiscuous
mode is disabled, the broadcast address is rejected.
If external loopback is used, the FCS logic must be allo-
cated to the receiver (by setting the DXMTFCS bit in
CSR15, and clearing the ADD_FCS bit in TMD1) when
using multicast addressing.
PADR
This 48-bit value represents the unique node address
assigned by the ISO 8802-3 (IEEE/ANSI 802.3) and
used for internal address comparison. PADR[0] is the
first address bit transmitted on the wire, and must be
zero. The six hex-digit nomenclature used by the ISO
8802-3 (IEEE/ANSI 802.3) maps to the PCnet-32 con-
troller PADR register as follows: the first byte comprises
PADR[7:0], with PADR[0] being the least significant bit
of the byte. The second ISO 8802-3 (IEEE/ANSI 802.3)
byte maps to PADR[15:8], again from LS bit to MS bit,
and so on. The sixth byte maps to PADR[47:40], the LS
bit being PADR[40].
MODE
The mode register in the initialization block is copied into
CSR15 and interpreted according to the description of
CSR15.
Receive Descriptors
When SSIZE32 = 0 (BCR20[8]), then the software struc-
tures are defined to be 16 bits wide, and receive descrip-
tors look as shown in Table 59.
Table 59. Receive Descriptor (SSIZE32 = 0)
Descriptor
Designation
Address
Bits 15-0
Bits 15-8
Bits 7-0
CRDA+00
RMD0
RMD0[15:0]
CRDA+02
RMD1
RMD1[31:24]
RMD0[23:16]
CRDA+04
RMD2
RMD1[15:0]
CRDA+06
RMD3
RMD2[15:0]
PCnet-32
Descriptor Designation
LANCE/
PCnet-ISA
PCnet-32 reference names within the table above refer
to the descriptor definitions given in text below. Since
the text descriptions are for 32-bit descriptors, the table
above shows the mapping of the 32-bit descriptors into
the 16-bit descriptor space. Since 16-bit descriptors are
a subset of the 32-bit descriptors, some portions of the
32-bit descriptors may not appear in Table 59.
When SSIZE32 = 1 (BCR 20[8]), then the software
structures are defined to be 32 bits wide, and receive
descriptors look as shown in Table 60.