am79c960 Advanced Micro Devices, am79c960 Datasheet - Page 80

• Manufacturer Part Number: am79c960
• Description: Pcnettm-isa Single-chip Ethernet Controller
• Manufacturer: Advanced Micro Devices

Note that bit 13 of TMD1, which was formerly a reserved
bit in the LANCE (Am7990), is assigned a new meaning,
ADD_FCS.
TMD0
Holds LADRF [15:0]. This is combined with HADR [7:0]
in TMD1 to form a 24-bit address of the buffer pointed to
by this descriptor table entry. There are no restrictions
on buffer byte alignment or length.
TMD1
Bit
15
14
13
12
11
1-422
AMD
ADD_FCS
MORE
Name
OWN
ERR
ONE
This bit indicates that the de-
scriptor entry is owned by the
host
PCnet-ISA controller (OWN=1).
The host sets the OWN bit after
filling the buffer pointed to by the
descriptor entry. The PCnet-ISA
controller clears the OWN bit af-
ter transmitting the contents of
the buffer. Both the PCnet-ISA
controller and the host must not
alter a descriptor entry after it has
relinquished ownership.
ERR is the OR of UFLO, LCOL,
LCAR, or RTRY. ERR is written
by the PCnet-ISA controller. This
bit is set in the current descriptor
when the error occurs, and there-
fore may be set in any descriptor
of a chained buffer transmission.
ADD_FCS dynamically controls
the generation of FCS on a frame
by frame basis. It is valid only if
the STP bit is set. When
ADD_FCS is set, the state of
DXMTFCS is ignored and trans-
mitter
activated. When ADD_FCS = 0,
FCS generation is controlled by
DXMTFCS. ADD_FCS is written
by the host, and unchanged by
the PCnet-ISA controller. This
was a reserved bit in the LANCE
(Am7990).
MORE indicates that more than
one re-try was needed to trans-
mit a frame. MORE is written by
the PCnet-ISA controller. This bit
has meaning only if the ENP or
the ERR bit is set.
ONE indicates that exactly one
re-try was needed to transmit a
frame. ONE flag is not valid when
LCOL is set. ONE is written by
the PCnet-ISA controller. This bit
(OWN=0)
FCS
Description
generation
or
P R E L I M I N A R Y
by
Am79C960
the
is
10
9
8
7-0
TMD2
Bit
15-12 ONES
11-0
HADR
BCNT
Name
ENP
DEF
STP
has meaning only if the ENP or
the ERR bit is set.
DEFERRED indicates that the
PCnet-ISA controller had to defer
while trying to transmit a frame.
This condition occurs if the chan-
nel is busy when the PCnet-ISA
controller is ready to transmit.
DEF is written by the PCnet-ISA
controller. This bit has meaning
only if the ENP or ERR bits are
set.
START OF PACKET indicates
that this is the first buffer to be
used by the PCnet-ISA controller
for this frame. It is used for data
chaining buffers. The STP bit
must be set in the first buffer of
the frame, or the PCnet-ISA con-
troller will skip over the descriptor
and poll the next descriptor(s)
until the OWN and STP bits are
set.
STP is written by the host and is
not changed by the PCnet-ISA
controller.
END OF PACKET indicates that
this is the last buffer to be used by
the PCnet-ISA controller for this
frame. It is used for data chaining
buffers. If both STP and ENP are
set, the frame fits into one buffer
and there is no data chaining.
ENP is written by the host and is
not changed by the PCnet-ISA
controller.
The HIGH ORDER 8 address
bits of the buffer pointed to by this
descriptor. This field is written by
the host and is not changed by
the PCnet-ISA controller.
MUST BE ONES. This field is
written by the host and un-
changed
controller.
BUFFER BYTE COUNT is the
length of the buffer pointed to by
this descriptor, expressed as the
two’s com- plement of the length
of the buffer. This is the number
of bytes from this buffer that will
be transmitted by the PCnet-ISA
controller. This field is written by
the host and is not changed by
Description
by
the
PCnet-ISA