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13 Ethernet
Switch
Send
Receive
pause
pause
packet
packet
(4) Automatic MDIX functionality
The automatic MDIX functionality automatically switches between MDI and MDI-X. The
functionality enables communication via either a crossover cable or a straight cable, and is
available only when auto-negotiation is used. If the connection mode (full duplex or half
duplex) is fixed, MDI-X is always selected. The following table shows the MDI and MDI-X
pin mappings.
Table 13-15 MDI and MDI-X pin mappings
RJ45
MDI
Pin
1000BASE-
No.
T
1
BI_DA+
2
BI_DA-
3
BI_DB+
4
BI_DC+
5
BI_DC-
6
BI_DB-
7
BI_DD+
8
BI_DD-
Note 1:
For the 10BASE-T and 100BASE-TX cables, separate signal lines are used for
sending (TD) and reception (RD).
180
Remote device
Send
Receive
pause
pause
packet
packet
desired
desired
Enabled
Disabled
desired
100BASE-T
10BASE-T
X
TD+
TD+
TD-
TD-
RD+
RD+
Unused
Unused
Unused
Unused
RD-
RD-
Unused
Unused
Unused
Unused
Result of
auto-negotiation on
the Switch
Send
Receive
pause
pause
packet
packet
on
on
on
on
off
off
on
on
MDI-X
1000BASE-
100BASE-T
T
X
BI_DB+
RD+
BI_DB-
RD-
BI_DA+
TD+
BI_DD+
Unused
BI_DD-
Unused
BI_DA-
TD-
BI_DC+
Unused
BI_DC-
Unused
Flow control
operation
Is
Is
sendin
sending
g
regulated
regulat
on the
ed on
remote
the
device?
Switch
?
Yes
Yes
Yes
Yes
No
No
Yes
Yes
10BASE-T
RD+
RD-
TD+
Unused
Unused
TD-
Unused
Unused
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