If you're a hard-core techie, you're probably familiar with the often-arcane world of USB, RS232, RS485 and RS422 converters. This article is geared toward the more casual computer user who may need those interface protocols on the job and wonders what, exactly they are, and how to use them. So, let's talk about the serial interface in general, why serial connections continue to be important, and why reliable converters are often crucial.
Today, when we connect something to a computer, it likely uses USB, which stands for Universal Serial Bus. Computers from Apple and some other manufacturers may also have an IEEE 1394 "Firewire" interface, though with USB 2.0 so fast, IEEE 1394 is used less often now. We are also used to the various card slots, ranging from the original PC Card format (often combined with ExpressCard connectivity) to slots supporting CF cards, SD cards, the tiny microSD cards and a number of other formats. Most external peripherals -- such as hard disks, optical drives, mice, cameras, etc. - connect to computers via one of the above methods. Most, but not all.
That's because, for a variety of reasons, there is still a large number of applications and peripherals that use serial communication. Serial communication goes way back to the early days of computing and refers to a technology that sends data bit by bit in serial fashion. It is a simple, reliable, and time-tested means of electronic communication, and sort of a common denominator that can be used between just about any two pieces of electronic equipment. At its most basic, RS232 uses different voltage levels with respect to ground to communicate point-to-point at slow speeds over short distances. RS422 uses twisted pairs and communicates signals faster and over longer distances via negative and positive voltages. Since it uses two twisted pairs, RS-422 can communicate in both directions simultaneously. RS485, finally, works like RS422, but uses an addressing system (a bit like Ethernet) and therefore can communicate with multiple devices. There are also devices that use TTL (Transistor Transistor Logic).
While these serial technologies continue to be used in a wide range of computer, automation and other commercial and industrial applications, they are now considered "legacy" interfaces by the computer industry, or at least the consumer side of things. As a result, most modern laptops no longer have a serial connector, and even on desktops they are becoming less common. And even devices that have "legacy support," i.e. a 9-pin serial connector, generally only provide RS232 connectivity.
This is where protocol converters and adapters come into play. These converters come in various sizes and configurations and convert between RS-232, RS-422, RS-485, and TTL. There may also be a need to convert between the electrical signals generated by computers and fiber optic transmission methods used for high-speed/high bandwidth connections. Often it is just a matter of getting an adapter to convert between your computer's USB port to whatever serial protocol is needed. Other times conversions is a bit more complex and requires special insulation, gender changers, the ability to manually manipulate signals, or there may be other special considerations. All of this is doable, and there's a whole industry dedicated to making and selling whatever converter you need for your project.
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Chris Robertson is a published author of Majon
International. All Rights Reserved. Copyright 2009 (Wed Aug 19 2009)
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