
Am79C978A
125
When the APAD_XMT bit (CSR4,
bit11) is set to 1, the setting of
DXMTFCS has no effect.
If
ADD_FCS is clear for a particular
frame, no FCS will be generated.
If ADD_FCS is set for a particular
frame, the state of DXMTFCS is
ignored and a FCS will be ap-
pended on that frame by the
transmit circuitry. See also the
ADD_FCS bit in TMD1.
DXMTFCS
is
set
and
This bit was called DTCR in the
LANCE (Am7990) device.
This bit is read/write accessible
only when either the STOP or the
SPND bit is set.
2
LOOP
Loopback Enable allows the
Am79C978A controller to oper-
ate in full-duplex mode for test
purposes. The setting of the
full-duplex control bits in BCR9
have no effect when the device
operates in loopback mode.
When LOOP = 1, loopback is
enabled. In combination with
INTL and MIIILP, various loop-
back modes are defined as fol-
lows in Table 31.
Refer to
Loopback Operation
section for more details.
This bit is read/write accessible
only when either the STOP or the
SPND bit is set. LOOP is cleared
by H_RESET or S_RESET and is
unaffected by STOP.
1
DTX
Disable
Am79C978A controller not ac-
cessing the Transmit Descriptor
Ring and, therefore, no transmis-
sions are attempted. DTX = 0,
will set TXON bit (CSR0 bit 4) if
STRT (CSR0 bit 1) is asserted.
Transmit
results
in
This bit is read/write accessible
only when either the STOP or the
SPND bit is set.
0
DRX
Disable Receiver results in
the Am79C978A controller not
accessing the Receive De-
scriptor Ring and, therefore,
all receive frame data are ig-
nored. DRX = 0 will set RXON
bit (CSR0 bit 5) if STRT
(CSR0 bit 1) is asserted.
This bit is read/write accessible
only when either the STOP or the
SPND bit is set.
CSR16: Initialization Block Address Lower
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-0
IADRL
This register is an alias of CSR1.
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set.
CSR17: Initialization Block Address Upper
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-0
IADRH
This register is an alias of CSR2.
These bits are read/write acces-
sible only when either the STOP
or the SPND bit is set.
CSR18: Current Receive Buffer Address Lower
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-0
CRBAL
Contains the lower 16 bits of the
current receive buffer address at
which the Am79C978A controller
will store incoming frame data.
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.
Table 31.
Loopback Configuration
LOOP
0
0
1
INTL
0
0
0
MIIILP
0
1
0
Function
Normal Operation
Internal Loop
External Loop