What are teletypes?
A teleprinter (teletypewriter, teletype or TTY)
is an electromechanical device that can be used to send and receive
typed messages through various communications channels, in either point-to-point or point-to-multipoint configurations.
Initially they were used in telegraphy, which was developed in the late
1830s.
Teleprinters
could use a variety of different communication media. These included a simple
pair of wires; dedicated non-switched telephone circuits (leased lines); switched
networks that operated similarly to the public telephone network (telex);
and radio and microwave links (telex-on-radio, or TOR). A teleprinter
attached to a modem could also communicate through standard switched
public telephone lines. This latter configuration was often used to connect
teleprinters to remote computers, particularly in time-sharing environments.
How Teleprinters work?
The
teleprinter consists of a typewriter-like keyboard and a printer, powered by an electric motor. The two devices are coupled to the motor by clutches that
are brought into operation automatically when required. A message is sent by
typing on the keyboard. Each key stroke generates a sequence of coded
electrical pulses, which are then routed by electronic switching through an
appropriate transmission system to the destination. There a receiving
teleprinter decodes the incoming pulses and prints the message on paper. To
this basic electromechanical design, some modern teleprinters have added such
electronic devices as magnetic memory and video display.
Difference
between typewriter and teleprinter?
Typewriter is a mechanical device used to print text by
pressing keys that cause type to be impressed through an inked ribbon onto
paper while teleprinter is a combined electromechanical typewriter
and printer, often with an integrated paper tape reader/printer, connected to others or to a computer via the
telephone system.
Difference
between telex and fax?
Telex is public switched network of
teleprinters similar to telephone which is used for the purpose of text-based
messages. Whereas fax (short-form of facsimile) is a telephonic transmission of
scan printed materials including text and images through the telephone line.
Teletype Model 33 features:
The Teletype Model 33 is an
electro-mechanical teleprinter designed for light-duty office. It was
Introduced in 1963 and is one of the most popular terminals in the
data-communications industry. The MIL Mod 8 (and Mod 80) was designed to
interface with this specific teletype, hence why I have a page dedicated to it.
The Model 33 ASR (Automatic Send and Receive) has a built-in 8-level punched
tape reader and tape punch which allows the user to save and record programs.
Coding Scheme:
The two different
coding schemes have been used for teleprinters. The first was used in the beginning
of1920s was a variation of the Baudot Code,
in which letters, numbers, punctuation marks, and keyboard functions were
represented by 32 combinations of 5 “on” and “off” pulses. With the advent of
digital computers in the 1960s, a new coding scheme, the American Standard Code
for Information Interchange (ASCII), was developed and
came to be widely used by teleprinters. ASCII employed 7 code pulses and was
thus able to provide 128 combinations, giving a much more extensive range of
symbols that could be transmitted. Teleprinters utilizing the ASCII code could
transmit messages at speeds up to 150 words per minute, compared to 75 words
per minute for machines using the Baudot Code.
Baudot Code:
The Baudot code or International Teleprinter Code was invented by Emile Baudot in 1870. It is binary code which uses crosses and dots. It was used for teleprinter messages instead of the morse code and allowed to encode 2^5 characters
efficiently. Each character was preceded and followed by a bit to
announce its start and end.
ASCII Code:
ASCII stands for American Standard Code for Information
Interchange. It's a 7-bit character code where every single bit represents a
unique character. ASCII
is a 7-bit character set containing 128 characters. It contains the numbers
from 0-9, the upper- and lower-case English letters from A to Z, and some
special characters. The character sets used in modern computer and in too
Internet, are all based on ASCII code.
Extended ASCII Code:
Extended ASCII character are eight-bit or larger encoder that include
the standard seven-bit ASCII characters plus additional characters.
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