RJ-45

The RJ-45 connector is commonly used for network cabling and for telephony applications. It's also used for serial connections in special cases. Here's a look at it:

RJ-45 Connector

Pin out for Ethernet

Although used for a variety of purposes, the RJ-45 connector is probably most commonly used for 10Base-T and 100Base-TX Ethernet connections.

Pin #	Ethernet 10BASE-T 100BASE-TX	EIA/TIA 568A	EIA/TIA 568B or AT&T 258A
1	Transmit +	White with green strip	White with orange stripe
2	Transmit -	Green with white stripe or solid green	Orange with white stripe or solid orange
3	Receive +	White with orange stripe	White with green stripe
4	N/A	Blue with white stripe or solid blue	Blue with white stripe or solid blue
5	N/A	White with blue stripe	White with blue stripe
6	Receive -	Orange with white stripe or solid orange	Green with white stripe or solid green
7	N/A	White with brown strip or solid brown	White with brown stripe
8	N/A	Brown with white stripe or solid brown.	Brown with white stripe or solid brown

Because only two pairs of wires in the eight-pin RJ-45 connector are used to carry Ethernet signals, and both 10BASE-T and 100BASE-TX use the same pins, a crossover cable made for one will also work with the other.

Also, please note that it is very important that a single pair be used for pins 3 and 6. If one conductor from one pair is used for pin 3 and a conductor from another pair is used for pin 6, performance will degrade. See the following figure.

To learn more about Ethernet, check out Charles Spurgeon's Ethernet Reference.

RJ-45 Pinout for RocketPort

The following chart shows the pin out for RJ-45 connectors used on certain RocketPort serial interface cards (manufactured by Comtrol).

Pin	Name/Description
1	Request To Send
2	Data Terminal Ready
3	Ground
4	Transmit Data
5	Receive Data
6	Data Carrier Detect
7	Data Set Ready
8	Clear To Send

Pinouts for ISDN

Here's an ISDN BRI U port pinout for a Cisco 750 series router:

Pin	Function
1	Not used
2	Not used
3	Not used
4	U interface network connection (tip)
5	U interface network connection (ring)
6	Not used
7	Power (pass-through to S connector)
8	Ground (pass-through to S connector)

The following chart shows the pinout for RJ-45 connectors used on certain ISDN S/T interfaces. For more info, see ANSI T1.605.

Pin	Color	Name/Description
1	White/Orange	N/A
2	Orange	N/A
3	White/Green	Receive+
4	Blue	Transmit +
5	White/Blue	Transmit -
6	Green	Receive -
7	White/Brown	-48VDC (optional)
8	Brown	-48VDC Return (optional)

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