Re: 8-bit encodings and ASCII (was: Unicode conformant character encodings and us-ascii)

From: Jim Allan (jallan@smrtytrek.com)
Date: Sat May 17 2003 - 18:06:24 EDT

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    Pim BLockland posted:

    > James Kass schreef:
    >
    >>> Now this is true, because the controls have double meanings (e.g.
    > 0x0D
    >>> is both a carriage return and an eighth note).
    >>
    >> Is it? Isn't the eighth note simply a unique graphic used in the
    > DOS
    >> font to display a single glyph for 0x0D where appropriate?
    >
    > If it was, I presume they would have used a CR arrow for a picture
    > in that position. And they could have used other "control pictures"
    > for other codes below 0x20, such as a musical note for 0x07, etc.
    > The fact that they didn't, shows they just wanted to expand the
    > character set. That's why the pictures in those positions include
    > pargraph signs, bullets etc.
    > Besides, the original IBM PC BIOS had separate functions for those
    > two functionalities - characters or control codes (i.e. some
    > functions output an inverse white circle for a 0x0A, while others do
    > a line feed).

    A lot of printers could produce those control character alternates when
    in the correct mode.

    For example Hewlett Packard's PCL printer language has a command
    "ESC & p # X" in which "#" is to be replaced by the number of bytes for
    which you want printable characters to appear for any control codes
    rather than performing the control functions.

    See http://lprng.sourceforge.net/DISTRIB/RESOURCES/DOCS/pbpclimp.pdf and
    search for 5.4 for that command and also the "ESC Y" command which
    allows printing of all the printable characters assigned to control
    codes except the musical note symbol assigned to CR.

    An application translating a PCL file to another graphic format (such as
    PDF) and wishing to use Unicode characters in the destination format
    should recognize both the PCL ESC sequences which set different
    character sets and also recognize any Display Hidden Character commands.

    An MS-DOS/PC-DOS printable control character table probably should
    appear among vendor tables on the Unicode site.

    But I don't imagine there would be much use for it.

    Jim Allan

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