Articles Tagged ‘Pinouts’

Serial Direct Cable Connection, DB9, DB25, COM Ports and Pinouts

This article covers the popular serial ports on workstations, servers and laptop computers. We cover serial data transfer, port pinouts, port speeds, serial interface types (DB9 & DB25), null modem cables and much more.

The Serial Direct Connection is the one which utilizes the COM ports of your computers. Every computer has at least two COM ports, COM1 and COM2. The "COM" stands for "Communications". Its pinouts are a lot simpler when compared to the parallel port, but the speed is also a lot slower.

To give you an idea of how fast (or slow) a serial port is, at its best you will get around 12 to 14 KB per second. That's pretty slow when you're used to a network connection, but let me show you how serial data is transferred so you can also understand why it's a lot slower:

Transfer of data via serial port

Figure 1. Transfer of data via serial port

 

The above picture gives you an idea on how serial data is transferred. Each colored block that is numbered is sent from PC 1 to PC 2. PC 2 will receive the data in the same order it was sent, in other words it will receive data block 1 first and then 2, all the way to block 7. This is a pretty good representation of data flow in a serial cable. Serial ports transmit data sequentially over one pair of wires (the rest of the wires are used to control the transfer).

Another way you can think of it is like a one lane road where the road is wide enough to only fit one car at a time (one data block at a time in our example above) so you would imagine that the road cannot process several cars at one time.

The Serial Port

Most new computers have two COM ports with 9 pins each; these are DB-9 male connectors. Older computers would have one DB-9 male connector and one DB-25 male connector. The 25 pin male connector is pretty much the same as the 9 pin, it's just bigger.

Let's have a look at a serial port to see what we are talking about:

Physical Serial interface - DB-9 (usually COM1) and DB-25 (usually COM2)

Figure 2. Physical Serial interface - DB-9 (usually COM1) and DB-25 (usually COM2)

Different pinouts are used for the DB-9 and DB-25 connectors and we will have a look at them in a moment. Let's just have another quick look at the COM ports of a new computer:

cabling_dcc3

Figure 3. Serial ports (COM1 & COM2)

Notice the COM ports, they are both DB-9 connectors, there is no more DB-25! The connector above the two blue COM ports is an LPT or Parallel port.

Straight Thru UTP Cables

UTP Cabling - Straight-thru cable CAT5, CAT5eThis article covers the commonly known Unshielded Twisted Pair (UTP) cable and shows how many pairs the UTP Cat5, Cat5e, Cat6 & Cat7 cables consists of, the colour coding they follow, the different wiring standard that exist (T-568A & T-568B) plus the pin number designations for both standards.

We will be mainly focussing on the wiring of CAT5e & 6 cables as they are the most popluar cables around! We'll also cover wiring classic CAT1 phone cables. It is very important to understand UTP cabling standards and how to correctly terminate them.

Cabling is the foundation for a solid network, and implementing it correctly the first time will help avoid hours of frustration and troubleshooting. On the other hand, if you are dealing with a poorly cabled network, this knowledge will help you to find the problem and fix it more efficiently.

Wiring the UTP cables

We are now going to look at how UTP cables are wired. There are two popular wiring schemes that most people use today: the T-568A and T-568B. These differ only in which color-coded pairs are connected -- pairs 2 and 3 are reversed. Both work equally well, as long as you don't mix them. If you always use only one version, you're okay, but if you mix A and B in a cable run, you will get crossed pairs.

UTP cables are terminated with standard connectors, jacks and punchdowns. The jack/plug is often referred to as a "RJ-45," but that is really a telephone company designation for the "modular eight-pin connector" terminated with the USOC pinout used for telephones. The male connector on the end of a patch cord is called a "plug" and the receptacle on the wall outlet is a "jack."

Cabling - RG-45 Jack and RJ-45 Plug / Connector

Figure 1. A RG-45 Jack and RJ-45 Plug / Connector

 

As already mentioned, UTP has four twisted pairs of wires. The illustration shows the pairs and the color codes they have. As you can see, the four pairs are labeled:
UTP Colour codes and Pairs

Figure 2. Colour codes & Pairs of UTP CAT 5, CAT 5e, CAT6, CAT7 Cable

Pairs 2 and 3 are used for normal 10/100 Mbps networks, while pairs 1 and 4 are reserved. In Gigabit Ethernet, all four pairs are used.

The picture below shows the end of a CAT5e cable with an RJ-45 connector, commonly used to connect computers to a switch. It also shows a stripped CAT5e cable and identifies the four twisted pairs:

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