Mail Archives: djgpp/1998/07/06/19:03:24
Alan Bowler wrote:
>
> In article <359FFF58 DOT 71CE272E AT alcyone DOT com> Erik Max Francis <max AT alcyone DOT com> writes:
> >Luc Van der Veken wrote:
> >
> >> What exact character would be used in the papertape days to
> >> signal the end of a tape? Decennia ago I used them, but I don't
> >> remember.
> >>
> >> CTRL/Z - ETX (CTRL/C) - EOT (CTRL/D) - EM (CTRL/Y)?
> >>
> >> Or more than one, platform-dependent?
> >
> >EOT (0x04, ^D) is the "correct" one from the ASCII standard, since it
> >stands for "end of transmission." This is used (almost?) universally on
> >Unix systems,
>
> That does not make it correct. EOT had a particular function.
> It powered down the teletype to a standby state. The motor would
> stop turning, and so on real teletypes that mechanically did the
> serial decode this meant that the teletype could not even interpret
> characters on the line. The other end would wake up the teletype
> (start the motor running again) by sending a "long break"
On the big ASR TTY (model 30?) with a built-in modem, ^D would hang up
the phone. Shutting down the distributer motor would have been the
current-loop equivalent, and the "long break", created by holding down
the <break> key, had the current-loop effect of dialing in.
>
Up above ^Z, there is a whole group of separators, RS (record), FS
(file), GS (group), etc., up to one sometimes called "word separator"
but more often, <space>. It is not in the format effector group (CR, LF,
HT, VT, BS), nor is it in the first two "sticks", so I don't call
<space> a control character at all.
> The "correct" choice for end of file, was File Separator (FS,
> control-backslash), but Gcos is the only system I know that used that.
>
> Generally paper tape stuff didn't much use "end of file".
> A tape would be prepared with a set of chunks each ended by
> X-OFF (DC3, ctrl-S). The machine would send out X-ON (DC1 ctrl-Q)
> to start the paper tape reader going, and the reader would stop
> when it read the next X-OFF. Alternately, the machine use a timeout
> mechanism to decide when there was no more paper tape.
--
If my address has "x" or "z" in it, remove them to reply.
"I view the progress of science as ... the slow erosion of the
tendency to dichotomize." Barbara Smuts, U. Mich.
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