Data communication is fundamentally a simple operation. Point A sends information to Point B and Point B receives it. A slightly more complex, and more practical, system allows Point A to send information to and receive information from Point B, and vice versa. It is what lies between points A and B that has been the substance of data communication system development since before the personal computer, or any computer for that matter, was ever invented.

For example, consider several simple examples of data communication systems that have nothing to do with computers: Paul Revere used a very basic system, whereby one light in the tower signified the British were approaching by land, and two indicated they were approaching by sea. During a game of blind-man's-bluff, the subject hears a sound when he comes within a certain distance of an object, and nothing when he is out of range. To solve the problem of knowing when dishes in a dishwasher are clean or dirty, a family might decide to place a black magnet on the dishwasher when dirty dishes are put in, and then change it to a white magnet when the cleaning cycle is started, and return the black magnet after it is emptied. The one thing all these examples have in common is that they all use two-state systems of communication. A two-state system is one which uses only two possible values to transmit information--the lamp is on or it is off, there is a sound or there is silence, the magnet is black or white, etc. The way these values are combined allows complex messages to be transmitted using very simple tools.

Consider Morse Code, a two-state data communication system that functions very similarly to today's computerized data communication systems. Developed by Samuel E.B. Morse in the 19th century, Morse code uses electrical current to transmit a series of dashes and dots that represent letters of the alphabet, numbers, a comma and a period. A basic Morse Code transaction works as follows: A "message" is given to an operator who translates that message into dots and dashes (Point A), then the transmitting operator uses the telegraph key to send an electrical signal to the receiving operator at the desired location to indicate that a message is about to come through. The receiving operator (point B) sends back an acknowledgment that he is ready, and the transmitting operator then sends the message which the receiving operator takes down. When the message is completely transmitted, the transmitting operator signals to the receiving operator that he is done, and the transmission line is closed. The receiving operator then translates the code back into the original message, and delivers it to the designated recipient.

Clearly, in a system of this type, accuracy is extremely important. As only two characters--dot or dash--are used to create a code for an entire language system, the transmitting and receiving operators must be extremely accurate. (Indeed, it makes a big difference whether the message says "Give one million dollars to Ted" or "Give one million dollars to Ned"--an easy mistake to make using Morse code, as the letter T is "-" and the letter N is "-.") This system can only work if both sides of the data communication system know the code and can encrypt and decode messages. It is also essential that the transmitter not send faster than the receiver can takedown the information. Even using expert operators, static on the line could obscure the signals making a dash sound like a dot and thereby corrupting the message. Thus, it becomes obvious that the most important aspect of designing a data communication system is ensuring not only that Point B can receive and understand the data transmitted by Point A, but also that the data remain uncorrupted during transmission.

These are the very same concerns faced by computerized data communication system designers. Indeed Morse code is often though of as the forerunner of the computer's binary communication system. The binary system uses the numbers 0 and 1 as the symbols for transmission of data. Using position notation, any value is represented by a weighted series of 1s and 0s. Thus the decimal number "33" would be represented by "100001" (1x2⁵ + 0x2⁴ + 0x2³ + 0x2² 0x2¹ + 1x2⁰) .

The above is a simple example of binary coding, but the same system is used by computers to transmit complex text messages, complex graphics, and streaming video. In order to accurately transmit many different types of data, numerous interfaces and protocols have been created. When selecting the appropriate equipment for your data communication application, it is important to examine both your application and the communication peripherals that must be incorporated into the system. First, determine whether your application is best suited for a standalone system based on a single PC or whether you need networked solution that will enable ports to be used across a LAN or WAN. Also determine whether you need a portable system using a laptop computer, or a desktop PC or Server. After deciding upon your host computer, determine the ports available, and the type of expansion boards this computer can best accommodate. Then, decide which of those options will best meet the speed and versatility demanded by your application. Once you've selected an interface, you can then begin to look at the type of data communication adapter you will need. You must also consider the distance you will need between the communication peripherals and the host computer, as well as the data transfer speed required for your application to function properly. The number of peripherals you need to connect to the host computer is also important for determining how many ports must be added via expansion boards or hubs. The sections that follow provide detailed explanations of the options available at each step in the decision making process.

Application Type

The first step in assessing your data communication application is identifying which peripherals you will need and where you will need them. While in the past your choice of peripherals may have limited your options, today just about any serial or parallel device is available in portable form. And, with Serial Device Server technology, many of these devices can be networked for remote access by any number of users.

There are no set rules for deciding between portable and desktop systems, or stand-alone and networked systems. However, common sense is your best guide. If your application requires traveling to multiple locations to download data, such as accessing an airplane's flight recorder from the cockpit for use in fleet maintenance, then a portable system could be an appropriate choice. However, if you are using a central computer to service a network of touch screens in a restaurant, then a desktop system might best serve your needs. If you are attempting to install a network in a factory to monitor equipment for preventive maintenance, running wires may be a problem, making ruggedized ethernet-based serial device servers an ideal choice.

See Quatech Application Examples which cover a wide range of data communication systems. If you need help designing the optimal system for your application, contact one of Quatech's expert sales engineers. We'd be pleased to help.