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Serial RS-232, RS-485, RS-422 and TTL Converters
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ARTICLES
RS232, RS422, and RS485 Converters - Telling the Difference
The
difference
between
RS232,
RS422
and
RS485
converters
is
clear
as
day
to
an
electronic
data
communications
engineer
or
specialist,
but
to
the
rest
of
us
they
are
just
some
ancient
industry
standards
that
have
probably
all
been
replaced
by
USB
anyway.
Or
at
least
you
can
use
a
converter
to
deal
with
them.
The
latter
is
true,
but
the
former
really
isn't:
those
standards
are
very
much
alive
and
continue
to
be
used
in a
wide
variety
of
applications.
But
let's
take
a
look
at
the
backgrounds
of
those
standards.
RS-232, a standard of the Electronics Industries Association (EIA), has been around for over four decades. It goes back to the days where remote Teletype machines were connected to mainframes via modems. Communication between those DTE (Data Terminal Equipment) machines and DCE (Data Circuit-terminating Equipment) happened sequentially, one bit at a time. It was all slow and quite mechanical, with different voltage levels compared to ground, representing binary system ones and zeros. Serial communication is quite simple, but early on manufacturers experimented with various control signals, pin layouts and proprietary methods. With RS232, the EIA established a standard that minimized incompatibilities and made life a lot easier for information technology departments and anyone else involved with data communication.
RS232 turned out to be a very enduring standard that remained a primary means of data communication until the mid-1990s, and it is still being used today. There are, however, some inherent shortcomings and limitations to RS232, primarily in the areas of speed, reliability and flow control. The RS422 standard addresses some of those issues with two sets of twisted pairs that carry negative and positive voltages. The RS-422 standard offers speeds up to 10 megabits per second and the maximum connection distance is 4,000 feet. In addition, since it uses two twisted pairs, with RS-422 you can communicate in both directions simultaneously. However, RS-422 also has an important limitation: it is still a point-to-point protocol and therefore unsuitable for many multi-drop applications. This is where RS-485 comes in.
RS-485 works very much like RS422 in terms of speed and distance, also using twisted pairs and voltage differentials for serial binary data communication. However, unlike with RS-422, with RS485 devices are addressable (like in Ethernet) and therefore can communicate with multiple nodes (up to 32). RS-485 is therefore suitable for a variety of master/slave architecture connections and networks. With more addressable devices and each device being able to communicate bi-directionally, line termination becomes an issue and requires special consideration.
What it all boils down to is that these older serial communication standards are still being used. USB may have largely replaced RS232 serial connectivity in consumer products, but in many industrial and commercial systems, serial data communication remains very much alive. Which means that anyone dealing with serial communication products and systems will need not only an understanding of the standards and principles behind the standards, but also a tool chest of serial data converter products. That includes RS-232, RS-422 and RS-485, but also TTL and fiber optics converters and adapters.
RS-232, a standard of the Electronics Industries Association (EIA), has been around for over four decades. It goes back to the days where remote Teletype machines were connected to mainframes via modems. Communication between those DTE (Data Terminal Equipment) machines and DCE (Data Circuit-terminating Equipment) happened sequentially, one bit at a time. It was all slow and quite mechanical, with different voltage levels compared to ground, representing binary system ones and zeros. Serial communication is quite simple, but early on manufacturers experimented with various control signals, pin layouts and proprietary methods. With RS232, the EIA established a standard that minimized incompatibilities and made life a lot easier for information technology departments and anyone else involved with data communication.
RS232 turned out to be a very enduring standard that remained a primary means of data communication until the mid-1990s, and it is still being used today. There are, however, some inherent shortcomings and limitations to RS232, primarily in the areas of speed, reliability and flow control. The RS422 standard addresses some of those issues with two sets of twisted pairs that carry negative and positive voltages. The RS-422 standard offers speeds up to 10 megabits per second and the maximum connection distance is 4,000 feet. In addition, since it uses two twisted pairs, with RS-422 you can communicate in both directions simultaneously. However, RS-422 also has an important limitation: it is still a point-to-point protocol and therefore unsuitable for many multi-drop applications. This is where RS-485 comes in.
RS-485 works very much like RS422 in terms of speed and distance, also using twisted pairs and voltage differentials for serial binary data communication. However, unlike with RS-422, with RS485 devices are addressable (like in Ethernet) and therefore can communicate with multiple nodes (up to 32). RS-485 is therefore suitable for a variety of master/slave architecture connections and networks. With more addressable devices and each device being able to communicate bi-directionally, line termination becomes an issue and requires special consideration.
What it all boils down to is that these older serial communication standards are still being used. USB may have largely replaced RS232 serial connectivity in consumer products, but in many industrial and commercial systems, serial data communication remains very much alive. Which means that anyone dealing with serial communication products and systems will need not only an understanding of the standards and principles behind the standards, but also a tool chest of serial data converter products. That includes RS-232, RS-422 and RS-485, but also TTL and fiber optics converters and adapters.
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