Enquiry character

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This article is about computer communications. For the process of solving a problem, see Inquiry.

In computer communications, enquiry is a transmission-control character that requests a response from the receiving station[1] with which a connection has been set up.[2] It represents a signal intended to trigger a response at the receiving end, to see if it is still present. The response, and 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.

Teletype Model 33 answer-back drum (brown, lower center left) for coding inquiry response message.

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.[3][4]

The 5-bit ITA2 has an enquiry character, as do the later ASCII and EBCDIC.

DEC terminals from the 1970s and later respond to enquiry with the answerback message. 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.[5]

See also[edit]


  1. ^ ZDNet Definition for: Enquiry Character
  2. ^ ATIS Telecom Glossary
  3. ^ "ASR 33 Teletype Rear View of Main Assembly". 
  5. ^ PDP-8 Maintenance Manual, Digital Equipment Corp., F-87, 2/66, 1966; page 5-2.

External links[edit]