
Am79C971
131
10BASE-T receive polarity rever-
sal algorithm is disabled. Like-
wise,
when
DAPC = 0,
polarity reversal algorithm is en-
abled.
the
This bit only has meaning when
the 10BASE-T network interface
is selected.
Read/Write accessible only when
either the STOP or the SPND bit
is set.
10
MENDECL
MENDEC Loopback Mode. See
the description of the LOOP bit in
CSR15, bit 2.
Read/Write accessible only when
either the STOP or the SPND bit
is set.
9
LRT
(TMAU mode) Low Receive
Threshold. When LRT = 1, the in-
ternal twisted pair receive thresh-
olds are reduced by 4.5 dB below
the standard 10BASE-T value
(approximately 3/5) and the un-
squelch threshold for the RXD
circuit will be 180 mV to 312 mV
peak.
When LRT = 0, the unsquelch
threshold for the RXD circuit will
be the standard 10BASE-T value,
300 mV to 520 mV peak.
In either case, the RXD circuit
post squelch threshold will be
one-half of the unsquelch thresh-
old.
This bit only has meaning when
the 10BASE-T network interface
is selected.
Read/Write accessible only when
either the STOP or the SPND bit
is set. Cleared by H_RESET or
S_RESET and is unaffected by
STOP.
TSEL
(AUI mode) Transmit Mode Se-
lect. TSEL controls the levels at
which the AUI drivers rest when
the AUI transmit port is idle.
When TSEL = 0, DO+ and DO-
yield
“
zero
”
differential to operate
transformer
coupled
(Ethernet 2 and IEEE 802.3).
When TSEL = 1, the DO+ idles at
a higher value with respect to
DO-, yielding a logical HIGH state
(Ethernet 1).
loads
This bit only has meaning when
the AUI network interface is se-
lected.
Read/Write accessible only when
either the STOP or the SPND bit
is set. Cleared by H_RESET or
S_RESET.
8-7
PORTSEL[1:0]Port Select bits allow for software
controlled selection of the net-
work medium. See Table 26.
PORTSEL
10BASE-T and MII are ignored
when the ASEL bit of BCR2 (bit 1)
has been set to 1.
settings
of
AUI,
Read/Write accessible only when
either the STOP or the SPND 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, bit 2).
Read/Write accessible only when
either the STOP or the SPND bit
is set.