CSR66: Next Transmit Byte Count
Bit
Name
Description
Reserved locations. Written as
zeros and read as undefined.
Reserved locations. Read and
written as zeros.
Next Transmit Byte Count. This
field is a copy of the BCNT field of
TMD1 of the next transmit de-
scriptor.
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set. These bits
are unaffected by H_RESET,
S_RESET, or STOP.
CSR67: Next Transmit Status
Bit
Name
Description
Reserved locations. Written as
zeros and read as undefined.
Next Transmit Status. This field is
a copy of bits 31-16 of TMD1 of
the next transmit descriptor.
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set. These bits
are unaffected by H_RESET,
S_RESET, or STOP.
7-0
RES
Reserved locations. Read and
written as zeros. Accessible only
when either the STOP or the
SPND bit is set.
Bit
Name
31-16 RES
15-12 RES
11-0
NXBC
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set. These bits
are unaffected by H_RESET,
S_RESET, or STOP.
CSR74: Transmit Ring Counter
Description
Reserved locations. Written as
zeros and read as undefined.
Transmit Ring Counter location.
Contains a two’s complement bi-
nary number used to number the
current transmit descriptor. This
counter interprets the value in
CSR78 as pointing to the first de-
scriptor. A counter value of zero
corresponds to the last descriptor
in the ring.
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set. These bits
are unaffected by H_RESET,
S_RESET, or STOP.
CSR76: Receive Ring Length
Bit
Name
Description
Reserved locations. Written as
zeros and read as undefined.
Receive Ring Length. Contains
the two’s complement of the re-
ceive descriptor ring length. This
register is initialized during the
Am79C978 controller’s initializa-
tion routine based on the value in
the RLEN field of the initialization
block. However, this register can
be manually altered. The actual
receive ring length is defined by
the current value in this register.
The ring length can be defined as
any value from 1 to 65535.
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set. These bits
are unaffected by H_RESET,
S_RESET, or STOP.
31-16 RES
15-0
XMTRC
31-16 RES
15-0
NXST
31-16 RES
15-0
RCVRL
CSR72: Receive Ring Counter
Bit
Name
Description
Reserved locations. Written as
zeros and read as undefined.
Receive Ring Counter location.
Contains a two’s complement bi-
nary number used to number the
current receive descriptor. This
counter interprets the value in
CSR76 as pointing to the first de-
scriptor. A counter value of zero
corresponds to the last descriptor
in the ring.
31-16 RES
15-0
RCVRC
Am79C978
137
AMD [ ADVANCED MICRO DEVICES ]
