End-of-transmission character
Encyclopedia
In telecommunication
, an end-of-transmission character ( or EOT) is a transmission
control character
. Its intended use is to indicate the conclusion of a transmission that may have included one or more texts and any associated message
headings.
An EOT is often used to initiate other functions, such as releasing circuits, disconnecting terminals, or placing receive terminals in a standby
condition. Its most common use today is to cause a Unix
tty
driver to signal end of file and thus exit programs that are awaiting input.
In ASCII
and Unicode
, the character with the value 4 is EOT. It can be referred to as control-D, ^D in caret notation
.
in DOS. The DOS Control-Z byte is actually sent and/or placed in files to indicate where the text ends. In contrast the Control-D causes the Unix terminal driver to signal the EOF condition, which is not a character, while the byte has no special meaning if actually read or written from a file or terminal.
In Unix the end-of-file character (by default EOT) causes the terminal driver to make available all characters its input buffer immediately; normally the driver would collect characters until it sees an end-of-line character. If the input buffer is empty (because no characters have been typed since the last end-of-line or end-of-file), a program reading from the terminal reads a count of zero bytes. In Unix, such a condition is understood as having reached the end of the file.
This can be demonstrated with the cat
program on Unix
-based operating systems such as Linux
: Run the
If the terminal driver is in raw mode it no longer interprets control characters, and the EOT character is sent unchanged to the program, which is free to interpret it any way it likes. A program may then decide to handle the EOT byte as an indication that it should end the text, this would then be similar to how is handled by DOS programs.
manufacturers such as IBM
, Burroughs Corporation,
and the BUNCH
. Terminal transmission control protocols such as IBM 3270
Poll/Select, or Burroughs TD830 Contention Mode
protocol use the EOT character to terminate a communications sequence between two cooperating stations (such as a host multiplexer or
Input/Output terminal).
A single Poll (ask the station for data) or Select (send
data to the station) operation will include two round-trip send-reply operations between the polling station and the station being
polled, the final operation being transmission of a single EOT character to the initiating station.
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, an end-of-transmission character ( or EOT) is a transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
control character
Control character
In computing and telecommunication, a control character or non-printing character is a code point in a character set, that does not in itself represent a written symbol.It is in-band signaling in the context of character encoding....
. Its intended use is to indicate the conclusion of a transmission that may have included one or more texts and any associated message
Message
A message in its most general meaning is an object of communication. It is a vessel which provides information. Yet, it can also be this information. Therefore, its meaning is dependent upon the context in which it is used; the term may apply to both the information and its form...
headings.
An EOT is often used to initiate other functions, such as releasing circuits, disconnecting terminals, or placing receive terminals in a standby
Standby
Standby may refer to:*Standby , a list in which passengers may request to be placed on to request an earlier or more convenient flight....
condition. Its most common use today is to cause a Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
tty
TTY
TTY may stand for:* Teleprinter or Teletypewriter or Teletype Printer, a typewriter paired with an electronic communication channel, used for telecommunications or as a computer terminal....
driver to signal end of file and thus exit programs that are awaiting input.
In ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
and Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
, the character with the value 4 is EOT. It can be referred to as control-D, ^D in caret notation
Caret notation
Caret notation is a notation for unprintable control characters in ASCII encoding. The notation consists of a caret followed by a capital letter; this digraph stands for the ASCII code that has the numerical value equivalent to the letter's numerical value. For example the EOT character with a...
.
Meaning in Unix
The EOT character in Unix is different from the Control-ZControl-Z
In computing, is a control character in ASCII code, also known as the substitute character or a keyboard shortcut. Strictly speaking, is not a printable character at all but a code for control purposes, though it is sometimes rendered by two characters as ^Z. It is generated by pressing the key...
in DOS. The DOS Control-Z byte is actually sent and/or placed in files to indicate where the text ends. In contrast the Control-D causes the Unix terminal driver to signal the EOF condition, which is not a character, while the byte has no special meaning if actually read or written from a file or terminal.
In Unix the end-of-file character (by default EOT) causes the terminal driver to make available all characters its input buffer immediately; normally the driver would collect characters until it sees an end-of-line character. If the input buffer is empty (because no characters have been typed since the last end-of-line or end-of-file), a program reading from the terminal reads a count of zero bytes. In Unix, such a condition is understood as having reached the end of the file.
This can be demonstrated with the cat
Cat (Unix)
The cat command is a standard Unix program used to concatenate and display files. The name is from catenate, a synonym of concatenate.- Specification :...
program on Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
-based operating systems such as Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
: Run the
cat command with no arguments, so that it accepts its input from the keyboard and prints output to the screen. Type a few characters without pressing , then type . The characters you have typed to that point are sent to cat, which then writes them to the screen. If you type without typing any characters first, you terminate the input stream and the program ends. You may be able to get an actual EOT by typing and then .If the terminal driver is in raw mode it no longer interprets control characters, and the EOT character is sent unchanged to the program, which is free to interpret it any way it likes. A program may then decide to handle the EOT byte as an indication that it should end the text, this would then be similar to how is handled by DOS programs.
Usage in Mainframe Computer System Communications Protocols
The EOT character is used in legacy communications protocols by Mainframe computerMainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
manufacturers such as IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, Burroughs Corporation,
and the BUNCH
BUNCH
The group of mainframe computer competitors to IBM in the 1970s became known as the BUNCH: Burroughs, UNIVAC, NCR, Control Data Corporation, and Honeywell...
. Terminal transmission control protocols such as IBM 3270
IBM 3270
The IBM 3270 is a class of block oriented terminals made by IBM since 1972 normally used to communicate with IBM mainframes. As such, it was the successor to the IBM 2260 display terminal. Due to the text colour on the original models, these terminals are informally known as green screen terminals...
Poll/Select, or Burroughs TD830 Contention Mode
protocol use the EOT character to terminate a communications sequence between two cooperating stations (such as a host multiplexer or
Input/Output terminal).
A single Poll (ask the station for data) or Select (send
data to the station) operation will include two round-trip send-reply operations between the polling station and the station being
polled, the final operation being transmission of a single EOT character to the initiating station.