Enquiry character

In computer communications, an ENQ (enquiry character) is a signal that one station sends to another to see if it's active. The response, known as an answer-back code, can contain information like the station's identity, equipment type, or status.

To make enquiry signal responses easier, teleprinters had a programmable drum capable of storing a response message up to 22 characters long that was customized by removing certain drum tabs. Messages stored in the drum were transmitted by pressing the "Here is" key on a terminal's keyboard or when the enquiry was received. Some terminals turned off this answer-back feature because it conflicted with other functions. However, later terminals included features allowing users to configure an answer-back message to avoid this issue.

Enquiry characters exist in various character encoding systems, including 5-bit ITA2, ASCII (American Standard Code for Information Interchange), and EBCDIC (Extended Binary Coded Decimal Interchange Code). Enquiry characters were originally called WRU (who are you) for telegraphs and are represented differently depending on the encoding system.

Enquiry characters became part of the ASCII standard in 1963 as WRU and later changed to ENQ. The modern enquiry character is represented in ASCII and Unicode as hexadecimal 0x05 and EBCDIC as hexadecimal 0x2D. Below is an example of the enquiry character in the ITA (International Telegraph Alphabet).

Character, Computer acronyms, Control character, Hardware terms, Status, TLA, WRU