Serial Communication Speed and Distance Limits
When discussing RS232, RS422 and RS485 serial data communication protocols, questions that come up are related to the speed and distance limits of the various protocols. This directly impacts the choice of protocol and therefore warrants discussion.
If RS232's limitations are unacceptable, the solution is often using the RS-422 standard that was designed for higher speed (up to 100kbps) and longer distances (up to 4,000 feet). The maximum data rate of RS-422 is up to 10 mbps over short distances, rivaling Ethernet and USB speeds. How can RS-422 be faster and error-free over much longer distances? Primarily because the standard uses a "balanced" signal on twisted pair wires that is far more immune to interference. This is referred to as "differential" data communication. Ground shifts and most noise is easily recognized and rejected by the receiver. Where does RS-485 fit in? It is used in projects that have the same speed requirements that RS422 can deliver, but also need multiple drivers (as opposed to just one in a RS422 setup).
Are the 4,000 feet maximum cable length and 10 mbps speed for RS-422 and RS-485 hard limits? Not really. There are now transceivers that support up to 10 mbps over short distances, and fiber optics can greatly extend the functional length of serial data communication. Use the proper adapters, converters and transceivers, and serial data communication is far from dead.
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+Chris Robertson is a published author of Majon International. All Rights Reserved. Copyright 2014 (Wed Oct 21 2009) Majon International. Majon International is one of the worlds MOST popular internet marketing and internet advertising companies on the web. Visit their main business resource internet marketing web site at: http://www.majon.com