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Some teleprinters had a "programmable" drum, which could hold a 20- or 22-character message. The message was encoded on the drum by breaking tabs off the drum. This sequence could be transmitted upon receipt of an enquiry signal, if enabled, or by pressing the "Here is" key on the keyboard.
The 5-bit
Browser Test Page for Unicode Character 'ENQUIRY' (U+0005)
Control characters
computer communications
A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...
, enquiry is a transmission-control character
In computing and telecommunications, a control character or non-printing character (NPC) is a code point in a character encoding, character set that does not represent a written Character (computing), character or symbol. They are used as in-ba ...
that requests a response from the receiving station with which a connection has been set up. It represents a signal intended to trigger a response at the receiving end, to see whether it is still present. The response, an answer-back code to the terminal that transmitted the WRU (who are you) signal, may include station identification, the type of equipment in service, and the status of the remote station.
Some teleprinters had a "programmable" drum, which could hold a 20- or 22-character message. The message was encoded on the drum by breaking tabs off the drum. This sequence could be transmitted upon receipt of an enquiry signal, if enabled, or by pressing the "Here is" key on the keyboard.
The 5-bit ITA2
The Baudot code () is an early character encoding for telegraphy invented by Émile Baudot in the 1870s. It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the most common teleprinter code in use before ASCII. Each Chara ...
has an enquiry character, as do the later ASCII
ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
and EBCDIC
Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight- bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding si ...
.
In the 1960s, DEC routinely disabled the answerback feature on Teletype Model 33 terminals because it interfered with the use of the paper-tape reader and punch for binary data. However, the DEC VT100
The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special ...
terminals from 1978 responded to enquiry with a user-configurable answerback message,{{cite book , url=http://www.bitsavers.org/pdf/dec/terminal/vt100/EK-VT100-UG-001_VT100_User_Guide_Aug78.pdf , title=VT100 User Guide , date=August 1978 , publisher=Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...
, access-date=2014-12-15 , archive-date=2019-05-29 , archive-url=https://web.archive.org/web/20190529015724/http://bitsavers.org/pdf/dec/terminal/vt100/EK-VT100-UG-001_VT100_User_Guide_Aug78.pdf , url-status=live as did its successors.
See also
*C0 and C1 control codes
The C0 and C1 control code or control character sets define control codes for use in text by computer systems that use ASCII and derivatives of ASCII. The codes represent additional information about the text, such as the position of a cursor, ...
* Keepalive
A keepalive (KA) is a message sent by one device to another to check that the link between the two is operating, or to prevent the link from being broken.
Description
Once a TCP connection has been established, that connection is defined to be ...
References
External links
Browser Test Page for Unicode Character 'ENQUIRY' (U+0005)
Control characters