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C00002 00002	This writeup explains the Data Disc keyboard mapping commands and
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This writeup explains the Data Disc keyboard mapping commands and
the responsible-TTY mechanism used to make it work.

Not explained here is how to override the privacy flag that may
prevent some of these commands from working.  For details on
that, see MAGIC.ME[UP,DOC].


THE RESPONSIBLE TTY

The system keeps track of the physical terminal (keyboard)
responsible for each logical terminal.  The responsible terminal
is the terminal that last typed a character (while mapped) to the
logical terminal.  Escape commands that affect the physical
rather than the logical terminal (e.g., all mapping, video, and
audio commands) do not change the responsible terminal.

No one is responsible for an available terminal, unless the
terminal is a DD in the DD channel wait queue, in which case the
DD that put it there is responsible.


PRIVATE DATA DISCS

You cannot (except by MAGIC, see above) map or tie to a private
DD for which you are not responsible.  However, you can always
map and tie to those DDs for which you ARE responsible.  Thus, if
you map somewhere and say ESCAPE H (make private), you can still
map away and back despite the privacy flag you set.

When you are mapped to a DD that is suddenly made private by
someone else, you will be mapped back to the lowest-numbered DD
line that you are responsible for, if any, else to a free DD.

When you are tied (and not mapped) to a DD that is suddenly made
private by someone else, you get tied back to where you are
mapped.


VIRTUAL Data Discs ARE HERE!

A given DD keyboard has a fixed number, but the DD line which
that keyboard controls (is mapped to) is completely independent
of the keyboard's number.  When you type on an available DD, the
lowest numbered free DD line is given to you.

Now here are some DD mapping and tying commands.

ESCAPE # M maps your DD keyboard to the DD line whose number is
given in the command; also your DD screen is tied to the given DD
line's video map, so that you will see whatever the program
running on that DD line does to its DD screen.

ESCAPE M maps you to your "home" DD line.  Your home line (only
defined for DD terminals) is set by typing MAGIC M while mapped
to the line which you wish to be your home line.  Initially (and
if you never type MAGIC M), your home line is the first DD line
you use.  If your home line goes available, your home becomes the
lowest-numbered DD line you are responsible for.

BREAK M maps you to the next DD used by the programmer name that
is logged in on the DD line that you are currently mapped to.

BREAK # L ties your DD screen to the video map of the DD whose
line number is given in the command; your keyboard is left mapped
wherever it already was.  Thus you can continue typing to one DD
line while watching another.

BREAK L without an argument ties you back to the DD that you are
mapped to.

ESCAPE CALL gets you an available DD line and types CALL on it.
If there aren't any free DD channels, ESCAPE CALL puts you in the
DD wait queue and beeps you (after mapping you to an unused DD).
(If you were already in the queue, it doesn't map you but does
beep.  If it maps you to an unused DD but doesn't beep, it means
the queue is full--with about 27 entries!  Each keyboard may only
have one entry in the DD wait queue at a given time.)  You will
be beeped again when you get your new DD, but your keyboard
mapping will not be changed at that time; you can use BREAK R
(see below) to map to the new DD line.  (No CALL will have been
typed on the new DD line.)  You will have about 30 seconds to
claim the new DD line before it goes available.

BREAK CALL gets you out of the DD wait queue no matter where you
are mapped at the time (since you can only have one entry in the
queue).  This command beeps if and only if you were really in the
queue when you gave the command.

BREAK R maps you to the next DD you are responsible for,
including any in the DD queue.  Remember that anything you type
(while mapped) to a DD makes you responsible, even if what you
type is an ESCAPE command (that went to the DD line rather than
to your terminal--mapping, video, and audio commands don't claim
responsibility, but, e.g., ESCAPE W does).

αβCLEAR disavows responsibility for the DD that you are
mapped to.  If that DD is also your home, this disclaims it as
such and your home reverts to the lowest-numbered DD line that
you are responsible for.

ESCAPE [prg] (a weird one, notice) maps you to the DD line in use
by the lowest job number logged in with the programmer name prg.
Only letters and digits can occur in the programmer name
typed--any other character terminates the command, and the
mapping is done if and only if the terminating character is a
right bracket "]".  This command only works on DDs.  ESCAPE [ on
any other terminal does not gobble the following programmer name.

MAGIC [prg] overrides privacy and does ESCAPE [prg].