
Am79C965A
135
Read/write accessible only when
STOP bit is set. Cleared by
H_RESET or S_RESET and is
unaffected by STOP.
8-7 PORTSEL[1:0] Port Select bits allow for software
controlled selection of the network
medium.
PORTSEL settings of AUI and
10BASE-T are ignored when the
ASEL bit of BCR2 (bit 1) has been
set to ONE.
The network port configuration is
shown in Table 41.
Table 41. Network Port Configuration.
Refer to the section on General
Purpose Serial Interface for de-
tailed information on accessing
GPSI.
Read/write accessible only when
STOP bit is set. Cleared by
H_RESET or S_RESET and is
unaffected by STOP.
6
INTL
Internal Loopback. See the de-
scription of LOOP, CSR15-2.
Read/write accessible only when
STOP bit is set.
5
DRTY
Disable Retry. When DRTY =
“
1
”
,
PCnet-32 controller will attempt only
one transmission. If DRTY =
“
0
”
,
PCnet-32 controller will attempt 16
retry attempts before signaling a
retry error. DRTY is defined when
the initialization block is read.
Read/write accessible only when
STOP bit is set.
4
FCOLL
Force Collision. This bit allows the
collision logic to be tested. PCnet-32
controller must be in internal
loopback for FCOLL to be valid. If
FCOLL =
“
1
”
, a collision will be
forced
during
transmission attempts. A Retry Error
loop-back
will ultimately result. If FCOLL =
“
0
”
,
the Force Collision logic will be
disabled.
Read/write accessible only when
STOP bit is set.
3
DXMTFCS Disable Transmit CRC (FCS).
When DXMTFCS = 0, the
transmitter will generate and append
a FCS to the transmitted frame.
When DXMTFCS = 1, the FCS logic
is allocated to the receiver and no
FCS is generated or sent with the
transmitted frame. DXMTFCS is
overridden when ADD_FCS is set in
TMD1.
See also the ADD_FCS bit in TMD1.
If DXMTFCS is set and ADD_FCS is
clear for a particular frame, no FCS
will be generated. The value of
ADD_FCS is valid only when STP is
set. If ADD_FCS is set for a
particular frame, the state of
DXMTFCS is ignored and a FCS will
be appended on that frame by the
transmit circuitry.
In loopback mode, this bit deter-
mines if the transmitter appends
FCS or if the receiver checks the
FCS.
This bit was called DTCR in the
LANCE (Am7990).
Read/write accessible only when
STOP bit is set.
2
LOOP
Loopback Enable allows PCnet-32
controller to operate in full duplex
mode for test purposes. When
LOOP =
“
1
”
, loop-back is enabled. In
combination with INTL and
MENDECL, various loopback
modes are defined in Table 42.
Table 42. Loopback Modes.
Read/write accessible only when
STOP bit is set. LOOP is cleared by
PORTSEL[1:0]
ASEL
(BCR2[1])
Link Status
(of 10BASE-T)
Network
Port
0X
1
Fail
AUI
0X
1
Pass
10BASE-T
0 0
0
X
AUI
0 1
0
X
10BASE-T
1 0
X
X
GPSI
1 1
X
X
Reserved
LOOP
INTL
MENDECL
Loopback Mode
0
X
X
Non-Loopback
1
0
X
External Loopback
1
1
0
Internal Loopback
Include MENDEC
1
1
1
Internal Loopback
Exclude MENDEC