5 ms·
Not mentioned in the article is that ENQ is a standard ASCII character (0x05, and previously abbreviated WRU for “Who are you?”) that causes the device on the o
by kps 9y ago
Not mentioned in the article is that ENQ is a standard ASCII character (0x05, and previously abbreviated WRU for “Who are you?”) that causes the device on the other end of the line to send back its answerback message.
On electromechanical teletypes¹ the answerback message was ‘programmed’ by breaking off tabs from a rotating drum, like an inverse music box.
¹ https://en.wikipedia.org/wiki/Teletype_Model_33 https://en.wikipedia.org/wiki/Teletype_Model_33
- colanderman 9y agoCuriously, there's even a Unicode glyph representing the ENQ command: ␅ (This is part of the broader collection of C0 glyphs: https://en.wikipedia.org/wiki/Unicode_control_characters#Control_pictures https://en.wikipedia.org/wiki/Unicode_control_characters#Con...)
- kps 9y agoTwo, if you count ⊠. There was a nearly forgotten effort to define standard symbols for all the ASCII control characters — ANSI X3.32 aka ISO 2047¹ aka ECMA-17². ¹ https://en.wikipedia.org/wiki/ISO_2047 https://en.wikipedia.org/wiki/ISO_2047 ² https://www.ecma-international.org/publications/files/ECMA-ST-WITHDRAWN/ECMA-17,%201st%20Edition,%20November%201968.pdf https://www.ecma-international.org/publications/files/ECMA-S...
- dmix 9y agoI was curious how it worked and I found a picture of the answerback 'drum' where you break off tabs (lower left): http://www.pdp8.net/asr33/pics/main_back.shtml http://www.pdp8.net/asr33/pics/main_back.shtml > In the lower left is the answer back drum. By breaking off the little tabs where you program a 20 character sequence that the teletype can send when the "HERE IS" key is pressed or if enabled when the WRU (ENQ, ascii 5) character is received. It seems you actually break off the tabs, it's not just a repeatable customizable configuration.
- Animats 9y agoBreaking off the tabs is permanent on the low end Teletype Model 33, although you could get a new blank wheel. The high end Model 28 (5-bit) and Model 35 (8-bit) had a set of removable tines you could replace one character at a time.[1] It's a reminder of how painfully hard it was to store data, even in read-only form, prior to the 1970s. [1] https://youtu.be/0A1a9rW_XRs?t=315 https://youtu.be/0A1a9rW_XRs?t=315