Asynchronous Terminals and Printer Processes Programming Manual

TERMINAL PROGRAMMING CONSIDERATIONS
Conversational Mode
Backspace. The BACKSPACE key allows the terminal operator to
back up and reenter one or more mistyped characters. The
backspace function operates differently on different terminals.
On typical video terminals, the cursor backs up one position for
each backspace entered. On hard-copy devices that backspace, a
line feed and a backspace are issued for the first backspace
entered, and only a backspace is issued for each subsequent
backspace entered. On hard-copy devices that do not backspace,
a backslash (\) is printed for each backspace entered. This
operation is invisible to the application program.
Line Cancel. The line cancel character allows the terminal
operator to cancel and retype the current line. When the line
cancel character is typed, the file system writes a <CR><LF>
sequence to the terminal. This operation is invisible to the
application program.
End of File. The end of file (EOF) character allows the terminal
operator to signal the application process that no more data will
be entered. When EOF is typed, the current file operation is
considered complete. No data is transferred into the application
program buffer, zero is returned in the count-read parameter, and
the condition code indicator is set to CCG. The file system
writes <EOF>!<CR><LF> to the terminal.
Application-Defined Interrupt Characters. You can change the
interrupt characters for special applications by using SETMODE
9. For ATP6100 subdevices, you can do so by including the
INTCHAR attribute in a CMI ALTER SU command. The file-
system reaction to application-defined interrupt characters is as
follows:
• The file transfer is considered complete.
• No line feed or carriage return is sent to the terminal;
the next transfer to the terminal begins at the character
following the interrupt character.
• The interrupt character is transferred into the application
program's buffer along with the line image (if any).
• The count-read parameter includes the interrupt character.
Application-defined interrupt characters can be mixed with
system-defined characters. The following example illustrates the
way to combine them.
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