AM79C90JCTR AMD [Advanced Micro Devices], AM79C90JCTR Datasheet - Page 29

• Manufacturer Part Number: AM79C90JCTR
• Description: CMOS Local Area Network Controller for Ethernet (C-LANCE)
• Manufacturer: AMD [Advanced Micro Devices]

Bit
15
14
13
12
11
10
09
08
07:00
ADD_FCS
MORE
Name
HADR
OWN
ONE
ERR
ENP
DEF
STP
Description
This bit indicates that the descriptor
entry is owned by the host (OWN =
O) or by the C-LANCE (OWN = 1).
The host sets the OWN bit after filling
the buffer pointed to by this descrip-
tor. The C-LANCE clears the OWN
bit after transmitting the contents of
the buffer. Neither the host nor the C-
LANCE may alter a descriptor entry
after it has relinquished ownership.
ERROR summary is the “OR” of
LCOL, LCAR, UFLO or RTRY.
Setting ADD_FCS=1, instructs the
controller to append a CRC to this
transmitted frame, regardless of the
setting of the DTCR bit (bit 3 in the
Mode Register). The ADD_FCS bit
allows the controller to be configured
to append CRC on a per packet ba-
sis, when DTCR=1. ADD_FCS is
only valid when STP=1.
MORE indicates that more than one
retry was needed to transmit a
packet.
ONE indicates that exactly one retry
was needed to transmit a packet.
The ONE flag is not valid when
LCOL is set.
DEFERRED
C-LANCE had to defer while trying to
transmit a packet. This condition oc-
curs if the channel is busy when the
C-LANCE is ready to transmit.
START OF PACKET indicates that
this is the first buffer to be used by
the C-LANCE for this packet. It is
used for data chaining buffers. STP
is set by the host and is not changed
by the C-LANCE. The STP bit must
be set in the first buffer of the packet,
or the C-LANCE will skip over this
descriptor and poll the next descrip-
tor(s) until the OWN and STP bits
are set.
END OF PACKET indicates that this
is the last buffer to be used by the C-
LANCE for this packet. It is used for
data chaining buffers. If both STP
and ENP are set, the packet fits into
one buffer and there is no data
chaining. ENP is set by the host and
is not changed by the C-LANCE.
The HIGH ORDER 8 address bits of
the buffer pointed to by this descrip-
tor. This field is written by the host
and is not changed by the C-LANCE.
indicates
that
P R E L I M I N A R Y
the
Am79C90
Transmit Message Descriptor 2 (TMD2)
Bit
15:12
11:00
15
Name
BCNT
ONES
12 11
Description
Must be ones. This field is set by the
host and is not changed by the
C-LANCE.
BUFFER BYTE COUNT is the us-
able length in bytes of the buffer
pointed to by this descriptor ex-
pressed as a negative two’s comple-
ment number. This is the number of
bytes from this buffer that will be
transmitted by the C-LANCE. This
field is written by the host and is not
changed by the C-LANCE. The first
buffer of a packet has to be at least
100 bytes minimum when data
chaining and 64 byte (DTCR = 1) or
60 bytes (DCTR = 0) when not data
chaining.
AMD
17881B-31
BCNT
ONES
0
29