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Table 3 RJ-45 MDI port pinouts
Pin
10BASE-T/100BASE-TX 1000BASE-T
Signal Function Signal
Function
1
Tx+
Send data
BIDA+
Bi-directional data cable A+
2
Tx-
Send data
BIDA-
Bi-directional data cable A-
3
Rx+
Receive data
BIDB+
Bi-directional data cable B+
4
Reserved
—
BIDC+
Bi-directional data cable C+
5
Reserved
—
BIDC-
Bi-directional data cable C
6
Rx-
Receive data
BIDB-
Bi-directional data cable B-
7
Reserved
—
BIDD+
Bi-directional data cable D+
8
Reserved
—
BIDD-
Bi-directional data cable D-
Table 4 RJ-45 MDI-X port pinouts
Pin
10BASE-T/100BASE-TX 1000BASE-T
Signal Function Signal
Function
1
Rx+
Receive data
BIDB+
Bi-directional data cable B+
2
Rx-
Receive data
BIDB-
Bi-directional data cable B-
3
Tx+
Send data
BIDA+
Bi-directional data cable A+
4
Reserved
—
BIDD+
Bi-directional data cable D+
5
Reserved
—
BIDD-
Bi-directional data cable D-
6
Tx-
Send data
BIDA-
Bi-directional data cable A-
7
Reserved
—
BIDC+
Bi-directional data cable C+
8
Reserved
—
BIDC-
Bi-directional data cable C-
To ensure normal communication, the pins for sending data on one port should correspond to the
pins for receiving data on the peer port. When both of the ports on the two devices are MDI or MDIX,
a crossover Ethernet cable is needed. A cross-over cable connects devices of the same type. When
one port is MDI and the other is MDIX, a straight-through Ethernet cable is needed. A
straight-through cable connects devices of different types.
If an RJ-45 Ethernet port with MDI/MDIX autosensing enabled can automatically negotiate pin roles.
The RJ-45 Ethernet ports on the switch support MDI/MDIX. By default, MDI/MDIX is enabled on a
port.
Making an Ethernet twisted pair cable
1.
Cut the cable to length with the crimping pliers.
2.
Strip off an appropriate length of the cable sheath. The length is typically that of the RJ-45
connector.
3.
Untwist the pairs so that they can lie flat, and arrange the colored wires based on the wiring
specifications.