Library /sys$common/syshlp/tff$tfuhelp.hlb About TFF  *Conan The Librarian (sorry for the slow response - running on an old VAX)

                  Terminal Fallback Facility (TFF)

   The Open VMS Terminal Fallback Facility  (TFF) provides table-driven
   character conversion for terminals.  Conversions  are transparent to
   the  application  software  unless  explicit  inquiries  are  made).
   You can  choose  character conversion tables from a master character
   library, located on the system disk in:

   SYS$SYSTEM:TFF$MASTER.DAT

   Conversions  can  be  one character to many on output to a terminal,
   or one to one on input from a terminal.

   TFF does compose  character emulation on input,  and you can control
   which keys are  auto-compose keys.  TFF  allows users  with National
   Replacement  Character (NRC) set terminals to use software developed
   with the Digital multinational character set  (MCS), essentially the
   ASCII  character set plus 128 characters currently used by owners of
   NRC terminals around the world.