Cross Over Cable Pin-outs

• Document ID#: TEC_012
• Written: 01/12/98
• Last Updated: 08/13/98
• Author: JC & MF
• Product: Any Ethernet or Fast Ethernet product
• Description: Cross Over Cables for Ethernet Networks (10BaseT or 100BaseTX)

Problem:
In order to connect two hubs or two 10BaseT (or 100BaseTX) devices without a hub, you need to have a cross over cable. A cross over cable is also necessary when you have non-EtherWave equipped devices at both ends of a daisy-chain. The reason for adding a cross over cable to the chain is to allow both of the non-EtherWave devices to communicate if all of the other EtherWave devices are turned off.

Situation:
When connecting two hubs or two 10BaseT (or 100BaseTX) devices without a hub, the transmit data (TD) pins of one eight-pin connector must be wired to the receive data (RD) pins of the other, and vice versa. Note that the TD and RD signals on each pair of a 10BaseT segment are polarized, with one wire of each signal pair carrying the positive (+) signal, and the other carrying the negative (-) signal. For a cross over cable, make sure that you keep the polarities the same, i.e. TD(-) to RD(-), and TD(+) to RD(+). See diagram below.

10BaseT or 100BaseTX crossover cable

Solution:
You can purchase a 7-foot cross over cable from Farallon for $7.99 (part number TE471). However, this cable should only be used for 10BaseT, NOT 100BaseTX, because it is rated as Category 3. If you need a longer cable, or a Category 5 cable for 100BaseTX, you should be able to purchase one from any computer reseller familiar with networking. Or if you want to build one of your own, the information you need can be found below.

10BaseT uses two pairs of 24-gauge solid copper (not stranded) wire. Each pair is twisted five to twelve times per foot. You can usually determine that a pair of wires form a twisted pair by the coloring of the wires. A wire with the color orange/ white is paired with the white/ orange wire. In some cases, one of the wires may be a solid color, i.e. green will be paired with the white wire that has a green stripe (white/green).

A normal 10Base T cable:
1 <--> 1 \
2 <--> 2 / 1 & 2 must be a twisted pair

3 <--> 3 \
6 <--> 6 / 3 & 6 must be a twisted pair

A crossover cable:
1 <--> 3 \
2 <--> 6 / these two must be a twisted pair

3 <--> 1 \
6 <--> 2 / these two must be a twisted pair

The numbers refer to the position in the eight-position RJ-45 connector. These positions are numbered from left to right when you are holding the connector pointing up, as if you were about to plug it into the ceiling, with the plastic clip away from you.

In summary, you should use a cross over cable to connect directly from one transceiver to another transceiver, or from one hub to another hub, or in an EtherWave daisy-chain where you have non-EtherWave devices at both ends of the chain.

For more information about Ethernet cables and Pin-outs, see: TEC_011 Ethernet Cabling and Pin Positions.