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Combining Legacy and Contemporary Serial Communication Systems

Although USB has replaced older serial data communication protocols in most consumer computing products, RS232, RS422, and RS485 are alive and well, just as older programming languages such as Cobol, Fortran, Algol and Pascal are largely gone from view, but are still widely used in millions of legacy (and many new) applications around the world. In fact, there are still many data communications projects where the lower cost, simpler implementation and greater flexibility of those serial communication protocols outweighs the plug-and-play simplicity of USB, and that's why there's a whole industry offering data conversion products that make USB to serial conversion (USB to RS485, USB to RS232, RS232 to RS485, etc.) and RS232 over Ethernet simple.

Why is serial data communication still so popular? There are many reasons, but first let's reiterate what those older data communication standards are all about, where they (still) excel, and where they have been replaced with newer standards (such as USB or Ethernet).

RS232, as defined by the Electronics Industries Association (EIA) was adopted more than 40 years ago as a way to standardize modem communication between teletype terminals to mainframe computers. The standard was based on comparing different voltage levels to ground, and use that to represent binary ones and zeros. This worked quite well for the slow communication speeds of that era, but as technology advanced, it became obvious that RS232 had limitations in speed, flow control and reliability that, while acceptable in many applications, called for additional standards that addressed those issues.

One answer was RS-422, a standard that takes uses twisted pairs to carry positive and negative voltages. Between using what are called "balanced" signals and twisted pairs wiring that is inherently less susceptible to electromagnetic interference, RS422 could handle much longer distances (up to 4,000 feet) and higher speeds (up to 100kbps, and up to 10 mbps over short distances). Even today, this type of "differential" data communication that allows easy detection of ground shifts and noise is often a quick and inexpensive answer for many projects.

RS485 is different from RS232 and RS422 insofar as it doesn't mandate a specific data protocol or specific pinouts (like the DB9 or DB25 connectors). Instead, RS485 provides a standardized way for drivers and receivers to interact in digital multipoint systems that can handle up to 32 drivers and 32 receivers, and more with repeaters. This makes RS-485 an important network standard for many technical/industrial applications such as data acquisition, device control, remote systems management and similar network tasks.

Over the years and decades, the original RS232 serial standard has therefore grown to include complementary standards that provide higher speed, reliability and flexibility, as well as numerous hybrid applications such as serial over Ethernet or USB to serial communication that are all connected via inexpensive and readily available serial adapters, serial converters, etc., and make such projects simple and affordable.

What all of this means is that incorporating legacy and contemporary data products often provides flexible, versatile solutions that get the job done and may result in significant cost savings.

To learn more about serial communication, products and support please go to www.USconverters.com


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