Twisted-pair Cable and Connector Pin-outs

100Mb/10BaseT

Different types of equipment that have 10BaseT ports can be configured as MDI or MDI-X. Connecting between these two different types of ports requires two different types of cables. Straight-through or crossover.


To make the crossover cable, one must first understand the basics of the straight-through cable.


Straight-through Cable

A "straight-through" cable should be used when connecting two ports that are not set to the same MDI mode. (i.e. PC to server hub). This is what you'll normally find at the store.

A straight-through cable has each internal twisted pair of wires connected to the same pin number at each end. Each twisted-pair wire set must be twisted through-out the entire length of the cable.

Straight-through Cable Pin-out

Straight Cable

10BaseT Cable Pin-Out

Pin

Signal

Color

1

T2

Org

2

R2

Org/Wht

3

T3

Wht/Grn

4

R1

Blu

5

T1

Wht/Blu

6

R3

Grn

7

T4

Wht/Brn

8

R4

Brn

 
  • Pins 1 and 2 must be a twisted pair.
  • Pins 3 and 6 must be a twisted pair.
  • Pins 4, 5, 7, and 8 are not used in this application, although they may be wired in the cable.

Crossover Cable

For cabling a MDI port to another MDI port, (i.e. Direct PC to PC) use a crossover connecting cable.

Crossover Cable Pin-Out

To make a crossover cable (for use between 2 computers without a concentrator), swap the Tx and Rx pairs - orange and green - 1,2 and 3,6. This would make the pinouts at one end as follows:

Crossover Cable

Crossover Cable Pin-Out

Pin

Signal

Color

1

T3

Wht/Grn

2

R3

Grn

3

T2

Wht/Org

4

R1

Blu

5

T1

Wht/Blu

6

R2

Org

7

T4

Wht/Brn

8

R4

Brn

  • Pins 1 and 2 at A, must be a twisted pair wired through to pins 3 and 6, respectively, at B.
  • Pins 3 and 6 at A, must be a twisted pair wired through to pins 1 and 2, respectively, at B.
  • Pins 4, 5, 7, and 8 are not used in this application, although they may be wired in the cable.


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A short crossover cable can be made to adapt a straight-through to a twisted-pair cable. I used a piece of 6" UTP cable, crimped J-45's at each end, and attached a double female adapter to one end (Radio Shack Part # 279-444). It works well.