
Am79C978
203
RFRTAG will be read as all zeros.
See the section on
Receive
Frame Tagging
for details.
15-12 ZEROS
This field is reserved. The
Am79C978 controller will write
zeros to these locations.
11-0
MCNT
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
Am79C978
controller
cleared by the host.
by
the
and
RMD3
Bit
Name
Description
31-0
US
User Space. Reserved for user
defined space.
Transmit Descriptors
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).
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)
12
11
TBADR[15:0]
MORE/
LTINT
1
Address
CXDA+00h
15
14
13
10
9
8
7-0
CXDA+02h
OWN
ERR
ADD_
FCS
1
EX
DEF
ONE
DEF
STP
ENP
TBADR[23:16]
CXDA+04h
1
1
BCNT
CXDA+06h
BUFF
UFLO
LCOL
LCAR
RTRY
TDR
Table 86.
29
Transmit Descriptor (SWSTYLE = 2)
27
26
25
TBADR[31:0]
Address
CXDA+00h
31
30
28
24
23
22-16
15-12
11-4
3-0
CXDA+04h
OWN
ERR
ADD_
FCS
EX
DEF
MORE/
LTINT
ONE
DEF
STP
ENP
BPE
RES
1111
BCNT
CXDA+08h
BUFF
UFLO
LCOL
LCAR
RTRY
RES
RES
RES
RES
RES
RES
TRC
CXDA+0Ch
USER SPACE
Table 87.
29
EX
DEF
ADD_
FCS
Transmit Descriptor (SWSTYLE = 3)
27
26
25
Address
31
30
28
24
23
22-16
15-12
11-4
3-0
CXDA+00h
BUFF
UFLO
LCOL
LCAR
RTRY
RES
RES
TRC
CXDA+04h
OWN
ERR
MORE/
LTINT
ONE
DEF
STP
ENP
BPE
RES
1111
BCNT
CXDA+08h
CXDA+0Ch
TBADR[31:0]
USER SPACE