■ FIGURE 2. An Arduino voltmeter.
you find this intriguing and want to help support your
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A Very Brief History of
There are some seriously oddball things about
USARTs and serial ports, mostly due to accidents of the
history and the evolution of serial communications, so let’s
first take a look at that history and get a feel for the origins
of some of the weirdness.
Why do we call the communication speed ‘baud
rate?’ Why does a serial connector have a ring indicator
pin? Why does a PC keyboard have a ‘Ctrl’ (control) key?
Frankly, a lot of the hardware and software
terminology for serial communications seems weird when
seen out of the context of how we arrived at today’s serial
communication techniques. This next section skims the
surface of a large topic primarily to show how some of the
terms we will be using came to be.
these serial tools available.
We looked at the PC side of the two-sided serial link
way back in Workshops 18, 19, and 20 (these are
www.nutsvolts.com). In those articles, we
learned how to write PC serial code in C# and Visual
Basic .NET. We created the Simple Terminal shown in
Figure 1 and we even learned how to write a GUI for an
Arduino-based voltmeter with a read-out on the PC as
shown in Figure 2.
The PC at one time had a UART to do serial
communications, but that is long gone in favor of USB. So
now, we have to use a virtual serial port on the PC side of
things. In fact, those three articles were excerpts from my
book Virtual Serial Port Cookbook where you can learn
how to use the FTDI FT232R to ease your
communications between a PC and a microcontroller. (If
Samuel F.B. Morse
Morse (Figure 3) patented the telegraph in 1840. The
name comes from the Greek tele = far away, and graphos
= writing. True to its name, the original telegraph machine
‘wrote’ with dots and dashes on paper.
Morse’s real invention was not the transmitter or
receiver — which were based on devices that were being
played with in electric laboratories of the time. His
contribution was a binary code (Figure 4) that allowed
characters to be sent as a serial stream of electric signals.
He made the most commonly used characters (such as A,
E, and T) into the simpler codes and the less commonly
used (such as Q, X, and Z) into the more complex code.
68 August 2011
■ FIGURE 3. Morse self-portrait (yes, he was an artist) and his telegraph machine.
In 1874, Emile Baudot (Figure
5) invented a five-bit binary code
that used a five-key transmitter. By
using mechanical clockworks, the
five bits were shifted out onto a
single wire and used by the
receiving station to print a character
on paper. Five bits can uniquely
encode 32 characters. Later
modifications to Baudot’s code
changed the code to 26 character
codes and 6 control codes. Two of
the control codes were used to
select either a 26 letter code or a
26 number/punctuation code table.
The remaining four control codes
were used for mechanical