perm filename DISPLA[3,2] blob sn#819413 filedate 1986-06-18 generic text, type T, neo UTF8
Most of the computer terminals directly attached to SAIL are display
terminals.  A few are vector-oriented displays called IIIs but the vast
majority use standard TV monitors and are called Data Discs or DDs.

These terminals use keyboards which generate an extended version of the usual
ASCII character set.  The normal 7-bit ASCII codes are all used for graphic
characters, and control functions are provided by two extra bits generated by
the CONTROL and META keys.  Thus, while the CONTROL key on a standard ASCII
terminal subtracts 100 (octal) from the character code, our CONTROL key adds
200 and our META key adds 400.  Also, two special keys, ESC (escape) and
BREAK, generate special codes which are not transmitted to user programs at
all, but are directly interpreted by the timesharing monitor as special
commands affecting the terminal.

These commands are explained at length in Section 2 of the Monitor Command
Manual, SAILON 54.3, which is available online in the file MONCOM.BH[S,DOC].
If you are logged in at a display terminal, you can print a concise list of
ESC and BREAK functions, and a table of the extended ASCII character codes,
on the Xerox Graphics Printer by typing HELP DDKEY if you are using a Data
Disc or HELP IIIKEY if you are using a III.  The list is designed to fit in
the indentation provided for this purpose at the top of the keyboard.

Certain other terminal types are supported as displays by the WAITS
system.  For details on support and use of such terminals, read the files
command HELP NOEDIT will tell you a little about using display terminals
that have no (parity-bit-controlling) "EDIT" key.

For more information about Datamedias, say HELP DM.  To get a crib sheet of
display commands for DMs, say HELP DMKEY.