History of Serial Communications
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Early serial communications methods
A smoke signal is a form of visual communication used over a long distance, developed both in the Americas and in China. By covering a fire with a blanket and quickly removing it, a puff of smoke can be generated. With some training, the sizes, shapes, and timing of these puffs can be controlled. Puffs may be observed from long distance, apparent to anyone within its visual range. With this in mind, signaling stations were often created to maximise the viewable distance. Stone bowls used by Native Americans and the towers of the Great Wall of China are examples of signaling stations.
As the signals were visible to all, unless they had a secretly understood significance they would be conveying the information alike to friend and enemy. There were, however, certain more or less recognized abstract smoke signals, of which the following are a few. One puff meant attention. Two puffs meant all's well. Three puffs of smoke, or three fires in a row, signifies danger, trouble, or a call for help.
There are two types of current loops, analog and digital. An example of analog current loop is 4-20 mA ("four to twenty milliamp current loop") where 4 mA represents 0% and 20 mA represents 100%. In a digital current loop, an absence of current represents high, and the presence of current represents low.
A communications current loop, as used in teletype/Baudot codes was 0-20mA/0-50mA on/off. Cryptographic teletype current loop ( the red side ) was/is 0-80uA due to electromagnetic snooping capabilities circa 1966 timeframe( TEMPEST program ).
The 4-20mA current loop is not a communications current loop but a process control standard for chemical/industrial sensors and actuators. The 4-20mA is analog and linear or square-root(rate of flow). The minimum 4mA is to get the low end above the noise level possible in an industrial enviroment. 4-20mA standard was developed so that the sourcing current had enough power to drive electromechanical devices at the receiving end of the current loop.
The first digital communications serial links required the sending unit to provide all the (current)loop power. The receiving devices were all electro-mechanical with the output a mechanical motion.
On the sea voyage home in 1832l, Samuel F.B. Morse encountered Charles Thomas Jackson of Boston who was well schooled in electromagnetism. Witnessing various experiments with Jackson's electromagnet, Morse developed the concept of a single wire telegraph. He was devising his telegraph code even before the ship docked. In time the Morse code would become the primary language of telegraphy in the world.
William Cooke and Professor Charles Wheatstone reached the stage of launching a commercial telegraph prior to Morse, despite starting later. In England, Cooke became fascinated by electrical telegraph in 1836, four years after Morse, but with greater financial resources. Cooke built a small electrical telegraph within three weeks. Wheatstone also was experimenting with telegraphy and (most importantly) understood that a single large battery would not carry a telegraphic signal over long distances, and that numerous small batteries were far more successful and efficient in this task (Wheatstone was building on the primary research of Joseph Henry, an American physicist). Cooke and Wheatstone formed a partnership and patented the electrical telegraph in May 1837, and within a short time had provided the Great Western Railway with a 13 km stretch of telegraph. However, Cooke and Wheatstone's multiple wire signaling method would be overtaken by Morse's superior code within a few years.
Morse encountered the problem of getting a telegraphic signal to carry over more than a few hundred yards of wire. His breakthrough came from the insights of Professor Leonard Gale, who taught chemistry at New York University (a personal friend of Joseph Henry). With Gale's help, Morse soon was able to send a message through ten miles (16 km) of wire. This was the great breakthrough Morse had been seeking.
Morse and Gale were soon joined by a young enthusiastic man, Alfred Vail, who had excellent skills, insights and money. Morse's telegraph now began to be developed very rapidly.
In 1838 a trip to Washington, D.C. failed to attract federal sponsorship for a telegraph line. Morse then traveled to Europe seeking both sponsorship and patents, but in London discovered Cooke and Wheatstone had already established priority. Morse would need the financial backing of Maine congressman Francis Ornand Jonathan Smith.
Morse made one last trip to Washington, D.C., in December 1842, stringing "wires between two committee rooms in the Capitol, and sent messages back and forth -- and, for some reason, this time some people believed him, and a bill was finally proposed allocating $30,000 towards building an experimental line".³
The general public was highly skeptical, and there were also a great many skeptics in Congress. A thirty eight-mile (61km) line was constructed between Washington, D.C., and Baltimore. The most convincing demonstration was when the results of the Whig National Convention at Baltimore in the spring of 1844 reached Washington via telegraph prior to the arrival of the first train. On 24 May, 1844 the line (which ran along the Baltimore and Ohio Railroad between the Capitol and Baltimore) was officially opened as Morse sent his famous words "What hath God wrought" along the wire.
In May 1845 the Magnetic Telegraph Company was formed in order to radiate telegraph lines from New York City towards Philadelphia, Boston, Buffalo, New York and the Mississippi.4
Morse also at one time adopted Wheatstone and Carl August von Steinheil's idea of broadcasting an electrical telegraph signal through a body of water or down steel railroad tracks or anything conductive. He went to great lengths to win a lawsuit for the right to be called "inventor of the telegraph", and promoted himself as being an inventor, but Alfred played an important role in the invention of the Morse Code, which was based on earlier codes for the electromagnetic telegraph.
Samuel Morse received a patent for the telegraph in 1847, at the old Beylerbeyi Palace (the present Beylerbeyi Palace was built in 1861-1865 on the same location) in Istanbul, which was issued by Sultan Abdülmecid who personally tested the new invention5
The Morse telegraphic apparatus was officially adopted as the standard for European telegraphy in 1851. Britain (with its British Empire) remained the only notable part of the world where other forms of electrical telegraph were in widespread use (they continued to use the needle telegraph invention of Cooke and Wheatstone).
Work on ASCII began in 1960. The first edition of the standard was published in 1963, a major revision in 1967, and the most recent update in 1986. It currently defines codes for 128 characters: 33 are non-printing, mostly obsolete control characters that affect how text is processed, and 95 are printable characters. (stub)
The non-printing ASCII codes were needed to actuate the teletype's mechanical mechanisms:
- line-feed, carrage-return, upper-lower case, etc.
The ASCII codes were re-coded to Baudot codes used by the mechanical teletype.
The teletype was the only standard I/O device until about 1970. From 1970 on, the teletype was the most economic hobby I/O due to the military surplus of teletypes.
The development of RS-232
The development of EIA-485 (RS-485)
The development of IEEE 1394 (FireWire)
The development of MIDI
The development of Universal Serial Bus (USB)
The development of Serial ATA (SATA)
- Istanbul City Guide: Beylerbeyi Palace
- "Franklin and his Electric Kite-Prosecution and Progress of Electrical researches--Historical Sketch of the Electric Telegraph--Claims of Morse and others--Uses of Electricity--Telegraphic Statistics.". New York Times. November 11, 1852, Wednesday. "It was in the month of June, 1752, a century ago, that Franklin made his celebrated experiment with the Electric Kite, by means of which he demonstrated the identity of electricity and lightning."