3 ms·
> It's a damn shame that the control characters for "Field Separator" (FS ASCII 28 decimal) and "Record Separator" (RS ASCII 30 decimal) weren't used instead of
by Animats 1y ago
> It's a damn shame that the control characters for "Field Separator" (FS ASCII 28 decimal) and "Record Separator" (RS ASCII 30 decimal) weren't used instead of TAB and CR/LF.
No, it's not.
That stuff is left over from 1940s-1950s schemes for polled multidrop teletype machines - multiple stations on one wire, taking turns.
The idea was that you punched paper tapes locally and then put them into a reader. When it was your station's turn, the central machine would send a polling sequence of a few characters, the selected reader would start up, read one message into the upstream system, then stop. In the other direction, the central station could send a turn-on code to any machine, print a message, then turn it off. Only one machine at a time could run. Those control characters were the delimiters for that process. All of this was mechanical, done by a unit called the "stunt box", which you can look up if really bored.
RS-485 is a descendant of that technology, still used in some industrial control systems.
(I used to restore antique Teletypes for fun, and had a functional Telegraph Office at steampunk conventions for about seven years.)
- rswail 1y agoWhy? The use of TTYs for computing interfaces is very different to using them as teletypes on comms links. I thought the control characters for that sort of use were the DC1-4 characters? RS-485 uses polling but my understanding is that the characters for polling usually involve like "FF" (hex) and some sort of device ID. I just read a TTY model 28 manual about the stunt box and I didn't see anything specific about FS/GS/RS there. How were messages delimited in the polled multidrop environment?
- varjag 1y agoTTY interfaces initially were teletypes on comms links.
- rswail 1y agoYes, but they were character based, not message based as being discussed. The ones I used were ASR-33s on 20mA current loop interfaces.
- dfox 1y agoModern protocols running over RS-485 UART usually use some kind of HDLC-inspired framing scheme with flag characters and byte stuffing. But still there is a lot of stuff that uses ASCII STX/ETX and then some kind of field separators inside otherwise human readable message. Things like industrial scales, industrial barcode readers and what not usually use something like that as default output format.
- Animats 1y ago> I just read a TTY model 28 manual about the stunt box and I didn't see anything specific about FS/GS/RS there. The Model 28 was a 5-bit Baudot (ITA2 code) machine with a stunt box. The Model 35, an ASCII machine, had a similar system, with different coding.[1] The term "Selective calling" replaced "stunt box". ASCII-67 is modern ASCII, but there was previously ASCII-63.[2] That keyboard has special keys for selective calling. WRU, RU, EOT, EOA, TAPE, ~TAPE, etc. Codes didn't become standardized industry-wide until ASCII-67. Before that, there were lots of variations. Here's a popular view of the process in the Baudot era.[3] That big switching center is essentially Sendmail built from of relays and paper tape equipment. It was called "Plan 55-A".[4] [1] https://www.smecc.org/teleprinters/35selcall001.pdf https://www.smecc.org/teleprinters/35selcall001.pdf [2] https://lostbits.net/blog/the-teletype-model-35-character-set.html https://lostbits.net/blog/the-teletype-model-35-character-se... [3] https://youtu.be/PKJyGuhCQdQ?t=369 https://youtu.be/PKJyGuhCQdQ?t=369 [4] https://en.wikipedia.org/wiki/Plan_55-A https://en.wikipedia.org/wiki/Plan_55-A
- ahazred8ta 1y agoHere's a pdf of a blank prop Western Union telegram form. Have you got others? https://www.hplhs.org/resources.php https://www.hplhs.org/resources.php
- Animats 1y agoI've used their fonts. Our telegram blanks were very similar, but custom.[1] [1] https://aether.ltd https://aether.ltd