T-568A Straight-Through Ethernet Cable

The TIA/EIA 568-A standard which was ratified in 1995, was replaced by the TIA/EIA 568-B standard in 2002 and has been updated since. Both standards define the T-568A and T-568B pin-outs for using Unshielded Twisted Pair cable and RJ-45 connectors for Ethernet connectivity. The standards and pin-out specification appear to be related and interchangeable, but are not the same and should not be used interchangeably.

T-568B Straight-Through Ethernet Cable

Both the T-568A and the T-568B standard Straight-Through cables are used most often as patch cords for your Ethernet connections. If you require a cable to connect two Ethernet devices directly together without a hub or when you connect two hubs together, you will need to use a Crossover cable instead.

RJ-45 Crossover Ethernet Cable

A good way of remembering how to wire a Crossover Ethernet cable is to wire one end using the T-568A standard and the other end using the T-568B standard. Another way of remembering the color coding is to simply switch the Green set of wires in place with the Orange set of wires. Specifically, switch the solid Green (G) with the solid Orange, and switch the green/white with the orange/white.

Ethernet Cable Instructions:

1. Pull the cable off the reel to the desired length and cut. If you are pulling cables through holes, its easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC’s cannot exceed 100 Meters (328 feet) for 100BASE-TX and 300 Meters for 10BASE-T.
2. Start on one end and strip the cable jacket off (about 1″) using a stripper or a knife. Be extra careful not to nick the wires, otherwise you will need to start over.
3. Spread, untwist the pairs, and arrange the wires in the order of the desired cable end. Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another, leaving only 1/2″ in wire length. If it is longer than 1/2″ it will be out-of-spec and susceptible to crosstalk. Flatten and insure there are no spaces between wires.
4. Hold the RJ-45 plug with the clip facing down or away from you. Push the wires firmly into the plug. Inspect each wire is flat even at the front of the plug. Check the order of the wires. Double check again. Check that the jacket is fitted right against the stop of the plug. Carefully hold the wire and firmly crimp the RJ-45 with the crimper.
5. Check the color orientation, check that the crimped connection is not about to come apart, and check to see if the wires are flat against the front of the plug. If even one of these are incorrect, you will have to start over. Test the Ethernet cable.

Ethernet Cable Tips:

• A straight-thru cable has identical ends.
• A crossover cable has different ends.
• A straight-thru is used as a patch cord in Ethernet connections.
• A crossover is used to connect two Ethernet devices without a hub or for connecting two hubs.
• A crossover has one end with the Orange set of wires switched with the Green set.
• Odd numbered pins are always striped, even numbered pins are always solid colored.
• Looking at the RJ-45 with the clip facing away from you, Brown is always on the right, and pin 1 is on the left.
• No more than 1/2″ of the Ethernet cable should be untwisted otherwise it will be susceptible to crosstalk.
• Do not deform, do not bend, do not stretch, do not staple, do not run parallel with power cables, and do not run Ethernet cables near noise inducing components.

Basic Theory:

By looking at a T-568A UTP Ethernet straight-thru cable and an Ethernet crossover cable with a T-568B end, we see that the TX (transmitter) pins are connected to the corresponding RX (receiver) pins, plus to plus and minus to minus. You can also see that both the blue and brown wire pairs on pins 4, 5, 7, and 8 are not used in either standard. What you may not realize is that, these same pins 4, 5, 7, and 8 are not used or required in 100BASE-TX as well. So why bother using these wires, well for one thing its simply easier to make a connection with all the wires grouped together. Otherwise you’ll be spending time trying to fit those tiny little wires into each of the corresponding holes in the RJ-45 connector.

]]> http://www.circuitxpert.com/blog/2009/04/ethernet-cable-color-coding-diagram/feed/ 0 http://www.circuitxpert.com/blog/2008/12/diodes-introduction/ http://www.circuitxpert.com/blog/2008/12/diodes-introduction/#comments Mon, 01 Dec 2008 23:11:04 +0000 Zaid http://www.circuitxpert.com/blog/?p=44

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The emitter is connected to zero volts and there is an increased emitter/base forward bias.

Base and collector currents increase.

There is more current through R1, a higher voltage drop across it, and a lower base voltage.

Since the collector current is higher there will be a larger voltage drop across R3.
The collector voltage will  be lower than normal.

The emitter voltage will of course be zero.

If the capacitor goes open circuit, the dc voltages will remain at their normal values.
However, the gain will be much reduced.

There is no potential divider action and the full +9 volts is applied to the base by R1.

This causes a high base current to flow, which in turn causes a high collector current to flow.

There is a large volts drop across R3, causing a low collector volts.

There is a large volts drop across R4, causing the emitter volts to rise.

With R1 o/c there is no voltage on the base, no base bias and no base current.

The transistor is OFF and there is no collector current and no voltage drop across R3.
The collector voltage will be the same as the supply volts, +9.

There is no current through R4, so there is no voltage drop across it.
The voltage at both ends is the same, zero volts.

There can be no base or collector current.

Since the current through R1 is less than normal, there will be a lower voltage drop across it and the base voltage will be higher than normal.

Since there is no current through R3 there will be no voltage dropped across it.
The voltage will be the same at both ends, and the collector will be at the supply voltage.

We would expect there to be no voltage across R4, but the meter connects the emitter to zero volts and some current flows through the meter.
The voltage indicated would depend upon the type of meter.

The base is still forward biased, so base current flows.

The base current will be higher than normal, because all the emitter current goes to the base and none to the collector.

Since there is more current through R1, there will be a higher voltage drop across it, and the base voltage will  be lower.

Since the emitter voltage is always about 0.6 volts lower than the base, it will read 0.1 volts.

We would expect the collector voltage to read zero, but we are actually reading the base voltage via the base/collector junction and it will read about 0.6 volts lower than the base.