RFRTAG will be read as all zeros.
See the section on Receive
Frame Tagging for details.
RMD3
Bit
Name
Description
31-0 US
User Space. Reserved for user
defined space.
15-12 ZEROS
11-0 MCNT
This field is reserved. The
Am79C978 controller will write
zeros to these locations.
Transmit Descriptors
Message Byte Count is the length
in bytes of the received message,
expressed as an unsigned binary
integer. MCNT is valid only when
ERR is clear and ENP is set.
MCNT is written by the
When SWSTYLE (BCR20, bits 7-0) is set to 0, the soft-
ware structures are defined to be 16 bits wide, and
transmit descriptors look like Table 85 (CXDA = Current
Transmit Descriptor Address).
When SWSTYLE (BCR 20, bits 7-0) is set to 2, the
software structures are defined to be 32 bits wide, and
transmit descriptors look like Table 86 (CXDA = Current
Transmit Descriptor Address).
Am79C978
controller
and
cleared by the host.
When SWSTYLE (BCR 20, bits 7-0) is set to 3, then the
software structures are defined to be 32 bits wide, and
transmit descriptors look like Table 87 (CXDA = Current
Transmit Descriptor Address).
Table 85. Transmit Descriptor (SWSTYLE = 0)
Address
15
14
13
12
11
10
9
8
7-0
CXDA+00h
TBADR[15:0]
ADD_
FCS
MORE/
LTINT
CXDA+02h
CXDA+04h
CXDA+06h
OWN
1
ERR
1
ONE
DEF
STP
ENP
TBADR[23:16]
1
1
BCNT
EX
DEF
BUFF
UFLO
LCOL
LCAR
RTRY
TDR
Table 86. Transmit Descriptor (SWSTYLE = 2)
Address
31
30
29
28
27
26
25
24
23
22-16 15-12
11-4
3-0
CXDA+00h
TBADR[31:0]
ADD_ MORE/
CXDA+04h OWN ERR
ONE
DEF
STP ENP
BPE
RES
RES
RES
1111
RES
BCNT
FCS
LTINT
EX
DEF
CXDA+08h BUFF UFLO
CXDA+0Ch
LCOL LCAR RTRY RES
RES
RES
TRC
USER SPACE
Table 87. Transmit Descriptor (SWSTYLE = 3)
Address
31
30
29
28
27
26
25
24
23
22-16 15-12
11-4
3-0
EX
DEF
CXDA+00h BUFF UFLO
CXDA+04h OWN ERR
LCOL LCAR RTRY
RES
RES
TRC
ADD_ MORE/
FCS LTINT
ONE
DEF
STP
ENP
BPE
RES
1111
BCNT
CXDA+08h
CXDA+0Ch
TBADR[31:0]
USER SPACE
Am79C978
203
AMD [ AMD ]
