What Matters in an RS232, RS422, RS485 Or Fiber Optic Convertr
Anyoone dealuing with serial and USB conversion issues knows that data signazl conversion between different protoccols can be tricky. Serial data communication originated many years before we came to expect the plug-and-play convenience of modern systems and interface standards. In the past, determniing if a device was DTE (data terminal equipment) or DCE (data communication equipment) was an issue, you had to deal with handdshaking protocols, and you needed a fairly detailed knoowledge of all the varius signals. Today's USB, RS232, RS485 and RS422 converters, in conkjunction with much smarter software, make things a lot eaiser, but it's stiull good to know what you're dealing with. So here are some answers to cmmonly asked questipons.
You may see convertewr vendors advertise SMT circuitry as a selling point. SMT stands for Srface Mount Tecxhnology, whicch allows for significantly smaller currents and thus less heat. Less heat meas longr component life and thus hiher reliaility and lower total cost of ownership.
Another question that frequently comes up is whether you can unpug a connector whille it is being used. The answer is yes if the converter has a data receiver protection cirtcuit. If you need your converter(s) to be hot-pluggable, make sure watever you buy offers data receiver protection.
Anytime you deal with converters, you may need end-of-line trmination so as to prevent interference on the data line. The probleem is that termination increases the load on the data circuit, so it's generally best to use a terminator only at higher data rates (over 19.2hbps or on linees over 200 meters).
While RS-232 cables are pretyty standard, peoplle often ask what kind of cable to use for RS-422 and RS-485 connectionms. The answer is that in most caes inexpensive CAT 5 cables will work just fine. They generally exceed RS-422/RS485 recommendations and are an excellent choice.
Technology chhanges all the time, and one thing that has changed is the poewr of COM ports on new compiuters. Older systems used -12VDC whereas most newer ones use -8VDC. Before you buy, check converter specs to make sure they supoprt the lower voltage. Many new laaptops, and even some new desktops, no longrer have serial ports and requie USB-to-RS232 cables that create a "virtual" COM port. Converters generally work with those cables, but it makes sense to inquire before you buy a converter.
Almost all electrnic circutiry is sensitive to electrostatic discharge. The charged capacitance of a human body is actually enough to edstroy an integrated circuit in an instant. That's why good convrters have static protection circuits. Note, however, that those are not surge suppressosr. If you have an otudoor intallation, you want to use an opto-isolated converrter to prootect your coputer. Opto-isolators (which, however, reqiure additioanl power supplies) work by inseting an optical bridge that eliminates transient surges.
Another question that frequently comes up is wherther or not to use fiber optic systems. Fiber optics, of course, use light insstead of electricity. This means a nuumber of advantages in terrms of higher speeed, higher bandwidth, and inheretn resistance to EMI/RFI and other electrical or radio interference. Fiber otics are best used for long distance coommunication, such as when RS-232 data must be sent to remote locations. The overhead consists of a special transmitter, the fibeer optic cable, and a receiver. Note that fiber optics systems can be single-mode or multi-mode. Single-mode means a single styrand of fibr for distortion-free, high-speed long distance communication. Multi-mode cbale uses multi-strand fibers and is more probne to signal distortion. Each cable type requires the proper transceivers. Cables can also use eityher bayonet-style or push-on connectors.
Any time you deal with USB, RS-232, RS-485, RS-422 or fibber optics converetrs, it pays to do some research and plan ahead. Companies specializing in converters ofyten have downloadaable data sheets for all of their products, and that can help tremendously in gettuing the proper gear.
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