Old ASCII (was: Re: Stupid CP/M question)

From: D. Peschel <dpeschel_at_u.washington.edu>
Date: Mon Jan 11 13:06:25 1999

> PET has a left arrow for that code as well. Sensible, since underscore is
> available elswhere in the character set (shift-$ IIRC) but I never knew it
> used to be standard ASCII. What other changes have there been? Is there
> any precedent for PET using up-arrow instead of circumflex?

Bingo! Yes, there is. That's the other major change.

There have been, I think, three major versions of ASCII. (Although ASCII
seems to be a very clear-cut standard, the history becomes very intricate if
you consider how ECMA, the US military, and possibly other standards bodies
got involved. Also, I think the character code itself, and the devices that
implemented it, influenced each other. So I don't know all the details.)

First version - 1963 (?) - This only had uppercase; the control characters
had slightly different names (which I don't have here -- sorry!) and code
176 octal was assigned to Escape. That's the reason why Hazeltine terminals
have so much trouble with tildes, by the way.

Second version - 1968 (?) - The one I mentioned. The same as ours except
for the underline being a left arrow and the caret being an upward-pointing
arrow. I think the control characters had their modern names

Third version - when? - This is the version I grew up with and consider
standard. It's the one found in zillions of ASCII charts. The standard
hides some interesting details, though:

        - You are allowed to use some characters as accents by overstriking.
          They are ' ` ~ ^ " and (I think) , as a cedilla.

        - There are a couple of other deliberate ambiguities. The tilde
          can be an overline and ^ can be another representation for the
          PL/I-style logical not. (These ambiguities could be in another
          version -- I hope I'm not getting confused here.)

Actually, I lied. There is a fourth version (it's an ISO standard or some-
thing). And there are international variants too. But since the fourth
verrsion is basically the same as the third version except for the names of
control characters (all the separators are now numbered), I don't really
consider it any different than the previous versions.

-- Derek
Received on Mon Jan 11 1999 - 13:06:25 GMT