AMD
P R E L I M I N A R Y
162
Am79C970A
A logical address is passed through the CRC generator,
producing a 32 bit result. The high order 6 bits of the
CRC is used to select one of the 64 bit positions in the
Logical Address Filter. If the selected filter bit is set,
the address is accepted and the frame is placed
into memory.
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 ZEROs
and promiscuous mode is disabled, all incoming logical
addresses except broadcast will be rejected.
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 com-
pared with the first bit in the destination address of the
incoming frame. It must be ZERO since only the destina-
tion address of a unicast frames is compared to PADR.
The six hex-digit nomenclature used by the ISO 8802-3
(IEEE/ANSI 802.3) maps to the PCnet-PCI II controller
PADR register as follows: the first byte is compared with
PADR[7:0], with PADR[0] being the least significant bit
of the byte. The second ISO 8802-3 (IEEE/ANSI 802.3)
byte is compared with PADR[15:8], again from the least
significant bit to the most significant bit, and so on. The
sixth byte is compared with PADR[47:40], the least sig-
nificant bit being PADR[40].
MODE
The mode register field of the initialization block is cop-
ied into CSR15 and interpreted according to the descrip-
tion of CSR15.
Receive Descriptors
When SWSTYLE (BCR20, bits 7–0) is set to ZERO,
then the software structures are defined to be 16
bits wide, and receive descriptors, (CRDA = Current
Receive Descriptor Address), are as shown in Table 40.
When SWSTYLE (BCR 20, bits 7–0) is set to ONE or
TWO, then the software structures are defined to be 32
bits wide, and receive descriptors, (CRDA = Current
Receive Descriptor Address), are as shown in Table 41.
When SWSTYLE (BCR 20, bits 7–0) is set to THREE,
then the software structures are defined to be 32 bits
wide, and receive descriptors, (CRDA = Current Re-
ceive Descriptor Address), are as shown in Table 42.
Table 40. Receive Descriptor (SWSTYLE = 0)
Address
CRDA+00h
CRDA+02h
CRDA+04h
CRDA+06h
15
14
13
12
11
RBADR[15:0]
CRC
10
9
8
7–0
OWN
1
0
ERR
1
0
FRAM
1
0
OFLO
1
0
BUFF
STP
ENP
RBADR[23:16]
BCNT
MCNT
Table 41. Receive Descriptor (SWSTYLE = 1,2)
Address
31
30
29
28
27
26
25
24
23
22
21
20
19–16
15–12
11–0
CRDA+00h
RBADR[31:0]
CRDA+04h
OWN
ERR
FRAM
OFLO
CRC
BUFF
STP
ENP
BPE
PAM
LAFM
BAM
RES
1111
BCNT
CRDA+08h
RCC
RPC
0000
MCNT
CRDA+0Ch
RESERVED
Table 42. Receive Descriptor (SWSTYLE = 3)
Address
31
30
29
28
27
26
25
24
23
22
21
20
19–16
15–12
11–0
CRDA+00h
RCC
RPC
0000
MCNT
CRDA+04h
OWN
ERR
FRAM
OFLO
CRC
BUFF
STP
ENP
BPE
PAM
LAFM
BAM
RES
1111
BCNT
CRDA+08h
RBADR[31:0]
CRDA+0Ch
RESERVED