BINARY FILE TRANSFERS WITH TALK

             A major deficiency of  Bob  Turkelson's  TALK  is  that  it
        cannot transfer binary files;  it works only on ASCII files, and
        will not always properly transfer some  ASCII  files.   See  the
        article  "Cheap  (Free?)  Networks", by David R.  Birkenmeyer in
        the Spring 83 DECUS Proceedings.

             CBA and CAB (_Convert _Blocks  to  _ASCII,  _Convert  _ASCII  to
        _Blocks)  circumvent  this  difficulty  by  making it possible to
        convert any file into an ASCII file.  The converted file may  be
        sent  to  a host VAX/VMS system and can then be reconverted back
        into the original form.  Both CAB and CBA will run under VMS  in
        compatibility mode.

             CBA and CAB can be invoked just like any  RSX  utility  and
        may  be  run  either  installed or uninstalled.  When installed,
        they may be invoked by:

        CBA outfile=infile
        CAB outfile=infile

        If they are not installed, they may be run with the RUN command:

        RUN CBA

        CBA will respond with

        CBA>

        and the user may then enter the command line.  CAB responds in a
        similar  manner.   The  commands  may also come from an indirect
        command file.  There are no switches, and  wild  cards  are  not
        allowed.   There  are no defaults for any element of the command
        line.

             CBA reads a file in block mode and converts each block into
        twelve  57-byte  ASCII  records.  The output file produced has a
        header record which contains  information  from  the  input-file
        file  header.  This record is followed by the ASCII translations
        of the input blocks.  Each group of  twelve  output  records  is
        followed  by  a checksum record twelve bytes long written with a
        2I6 format.  The first field should  always  contain  the  value
        512.   The  second field contains the checksum computed from the
        input block.
             The input file may be an ASCII file.  This is useful, since
        some  ASCII  files may be scrambled by TALK .  Output files from
        Digital Standard Runoff may be scrambled in transmission if they
        contain words emphasized by underlining or overstriking.

             CAB inverts the operation of CBA.  It reads a file produced
        by CBA and converts it back to the original form.  A checksum is
        computed for each  block  produced  and  is  compared  with  the
        transmitted  checksum.   If the checksums do not match, an error
        message is produced.

                                                                          Page 2


	     LIMITATIONS:

	     RMS files  are not  supported;  only the  part of  the file
	header used by FCS is translated. 

	________________________________________________________________

             Both CAB and CBA use subroutines from DECUS, without  which
        it would have been much more difficult to write them.
             The command line processing is done with  MACRO-11  modules
        from  Robert K.  Stodola.  The source code is well commented and
        should be read for more information.
             Block mode  I/O  is  done  with  routines  from  Philip  H.
        Cannon.   These  are  in  the object library DLIB.OLB.  Only the
        modules  used  are  documented  here.   See  INFO.DOC  for  that
        documentation.   See  the  Spring '80 RSX SIG tape [300,052] for
        more details.