- PROFESSIONAL QUALITY
- Serial Converters
- Isolated Converters
- USB Adapters
- Fiber Optic Media Converters
Serial and USB Converter Products
image,http://a3.websitealive.com/1469/Visitor/vButton_v3.asp?groupid=1469&departmentid=1795&w=400&h=400&icon_online=https%3A%2F%2Fimages%2Ewebsitealive%2Ecom%2Fimages%2Fhosted%2Fupload%2F25474%2Egif&icon_offline=https%3A%2F%2Fimages%2Ewebsitealive%2Ecom%2Fimages%2Fhosted%2Fupload%2F25476%2Egif,189,1795
Serial RS-232, RS-485, RS-422 and TTL Converters
USB Adapters - Fiber Optic Converters - Ethernet Converters
Guaranteed ExpressShipping on Time
ARTICLES
Serial Data Communication Basics: A Refresher
COBOL
programming
and
serial
data
communication
have
much
in
common.
There
was
a
time
when
the
COBOL
computer
language
ruled
the
business
programming
world
just
as
there
was
a
time
when
most
data
communication
used
serial
connections
and
the
RS232,
RS422
or
RS485
protocols.
But
just
like
newer
programming
languages
did
not
completely
replace
COBOL
and
there
are
still
hundreds
of
millions
of
lines
of
mission-critical
COBOL
code
in
use
all
over
the
world,
USB
and
other
high-speed
data
communications
protocols
did
not
simply
replace
RS232-style
serial
communication.
As a
result,
there
is
still
much
demand
for
serial
communication
protocol
skills
and
if
you're
in
that
line
of
business,
it
pays
to
know
all
about
those
older
standards
and
the
converters
and
adapters
used
to
interface
them
with
each
other
and
newer
protocols.
So for old time's sake and to keep from getting rusty, let's revisit what all is involved in designing or analyzing a simple serial cable that takes advantage of all the various aspects of the RS-232 standard (or RS-422 or RS-485).
First, there's speed, and here there are two aspects. One is that the speed of the sending and receiving devices must match. Buffering and flow control may come into play here. The other is maximum transmission speeds and how they relate to maximum cable length.
Second, there's flow control. This comes into play when one of the devices is much slower or may occasionally want to stop receiving. Flow control can be either via software (by using XON/XOFF or ETX/ACL signals) or via hardware by using one of the RS232 pins.
Third, there are parity (a simple way of error control), stop bits (enclosing characters with start and stop bits), and character length (there are different codes, and they may or may not include parity bits).
Fourth, serial communication can be in full-duplex, half-duplex or just simplex. The chosen mode can influence which connector pins are being used. Note that there is also "echoplexing," which is echoing characters back to the sender. Setting this wrong may result in no characters displayed or them being displayed twice.
Fifth, make sure line feeds are set properly so that text is properly formatted. This remains a big issue to this day, with different computers and operating systems handling line feeds in a different way.
Sixth, differentiate between synchronous and asynchronous data transmission. Synchronous uses a clock whereas asynchronous uses start and stop bits. Sometimes there is a combination of the two. What's important is that both ends are set the same way.
Finally, there's polarity. This refers to signals being either positive or negative. For example, hardware flow control may expect a positive signal on a pin, and it won't work if the signal is negative.
Not all of the above matter anymore in modern serial implementations as much is now automated and handled by sophisticated hardware and drivers. And when dealing with systems that include Ethernet, TTL, fiber optics and all the converters and adapters used in such systems, there are numerous other considerations. But knowing how it all works in RS232-style serial communication is a good thing, and refreshing one's memory beyond the brief listing in this article should almost be mandatory for anyone dealing with data communication.
So for old time's sake and to keep from getting rusty, let's revisit what all is involved in designing or analyzing a simple serial cable that takes advantage of all the various aspects of the RS-232 standard (or RS-422 or RS-485).
First, there's speed, and here there are two aspects. One is that the speed of the sending and receiving devices must match. Buffering and flow control may come into play here. The other is maximum transmission speeds and how they relate to maximum cable length.
Second, there's flow control. This comes into play when one of the devices is much slower or may occasionally want to stop receiving. Flow control can be either via software (by using XON/XOFF or ETX/ACL signals) or via hardware by using one of the RS232 pins.
Third, there are parity (a simple way of error control), stop bits (enclosing characters with start and stop bits), and character length (there are different codes, and they may or may not include parity bits).
Fourth, serial communication can be in full-duplex, half-duplex or just simplex. The chosen mode can influence which connector pins are being used. Note that there is also "echoplexing," which is echoing characters back to the sender. Setting this wrong may result in no characters displayed or them being displayed twice.
Fifth, make sure line feeds are set properly so that text is properly formatted. This remains a big issue to this day, with different computers and operating systems handling line feeds in a different way.
Sixth, differentiate between synchronous and asynchronous data transmission. Synchronous uses a clock whereas asynchronous uses start and stop bits. Sometimes there is a combination of the two. What's important is that both ends are set the same way.
Finally, there's polarity. This refers to signals being either positive or negative. For example, hardware flow control may expect a positive signal on a pin, and it won't work if the signal is negative.
Not all of the above matter anymore in modern serial implementations as much is now automated and handled by sophisticated hardware and drivers. And when dealing with systems that include Ethernet, TTL, fiber optics and all the converters and adapters used in such systems, there are numerous other considerations. But knowing how it all works in RS232-style serial communication is a good thing, and refreshing one's memory beyond the brief listing in this article should almost be mandatory for anyone dealing with data communication.
|
|
2006-2010 Copyright Protected - Sima S. Enterprises LLC - Terms & Conditions - Privacy Statement -
