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                 Data Interchange Library Beware File


                              July, 1986


                             VERSION 2.1





  COPYRIGHT (C) DIGITAL EQUIPMENT CORPORATION 1983, 1986.
  ALL RIGHTS RESERVED.
  
  THIS SOFTWARE IS FURNISHED UNDER A LICENSE AND MAY  BE  USED  AND
  COPIED ONLY IN ACCORDANCE WITH THE TERMS OF SUCH LICENSE AND WITH
  THE INCLUSION OF THE ABOVE COPYRIGHT NOTICE.   THIS  SOFTWARE  OR
  ANY  OTHER  COPIES  THEREOF MAY NOT BE PROVIDED OR OTHERWISE MADE
  AVAILABLE TO ANY OTHER PERSON.  NO TITLE TO AND OWNERSHIP OF  THE
  SOFTWARE IS HEREBY TRANSFERRED.
  
  THE INFORMATION IN THIS SOFTWARE IS  SUBJECT  TO  CHANGE  WITHOUT
  NOTICE  AND  SHOULD  NOT  BE CONSTRUED AS A COMMITMENT BY DIGITAL
  EQUIPMENT CORPORATION.
  
  DIGITAL ASSUMES NO RESPONSIBILITY FOR THE USE OR  RELIABILITY  OF
  ITS SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY DIGITAL.

                                                                Page 2


1.0  INTRODUCTION

This document supplements  the  Data  Interchange  Library  manual  by
pointing out hints and potential problems.

The  file  DIL.DOC  contains   further   supplemental   documentation,
including installation instructions.



2.0  TOPS-20 VERSION REQUIRED

You must be running TOPS-20 version 5.1 (or a  later  version),  which
incorporates several fixes to NSPSRV, in order to use the Task-to-Task
or Remote File Access routines on TOPS-20.  If you have  a  2020,  you
must run TOPS-20 version 4.1 (or a later version).



3.0  USER-ASSIGNABLE PA1050 INTERRUPT CHANNELS ON TOPS-20

There are no user-assignable interrupts in PA1050 left for  the  COBOL
user  on  TOPS-20  if the IP20 routines in TRAFFIC-20, the Remote File
Access routines, and the Task-to-Task routines are loaded in one  user
program, due to a PA1050 restriction.  Note that using user-assignable
interrupts in PA1050 is not supported.



4.0  REMOTE FILE ACCESS ROUTINES WITH FORTRAN-20

If FORTRAN programs using the Remote File Access routines get a  stack
overflow  problem,  the  user  should  rebuild  FOROTS  (according  to
instructions in the  Fortran  Installation  Guide),  to  increase  the
runtime stack space.

To use the rebuilt FOROTS, you must have FORLIB.REL and FOROT7.EXE  in
your SYS:  area.



5.0  USING A SHAREABLE OTS ON TOPS-20 AND TOPS-10

5.1  FORTRAN PROGRAMS ON TOPS-20

Normal loading of a FORTRAN program with DIL will result in  a  TWOSEG
program  with  a  nonshareable FOROTS loaded from FORLIB.  This can be
saved and executed in a shareable fashion.  If you want  to  load  the
DIL  code in the low segment so that the shareable FOROTS can be used,
you must use /SEG:LOW in the LINK command when loading  your  program.
For  more  information  on  the /SEG link switch, see the TOPS-20 Link
Manual.

                                                                Page 3


5.2  FORTRAN PROGRAMS ON TOPS-10

Normal linking of a TOPS-10 program, using the  instructions  provided
in  the  DIL  Manual, will cause the DIL code to always be loaded into
the low segment.  This means that you can  always  use  the  shareable
FOROTS.  For more information, see the DIL Manual.



5.3  COBOL PROGRAMS

COBOL  programs  will  normally   produce   low-address   data   areas
(containing  COBOL  and  DIL writeable data), higher-address pure code
areas   containing   COBOL   and   DIL   code,   and   the   shareable
COBLIB.REL/COBOTS-V13.EXE  (on  TOPS-20) or C74LIB.REL, C74O12.EXE (on
TOPS-10) which comes in at higher addresses.   This  behavior  can  be
modified  by  the  appropriate switches to the COBOL compiler (see the
TOPS-10/TOPS-20 COBOL Language Reference manual).



6.0  REMOTE FILE ACCESS TO TOPS-10/TOPS-20 FILES

All TOPS-10/TOPS-20 ASCII files  for  remote  file  access  should  be
specified  as  stream  record format with no record attributes or with
carriage-return/linefeed envelope attribute.



7.0  PRINT RECORD ATTRIBUTE FOR VMS FILES

Record attribute PRINT is only valid for record format VFC on the VAX.



8.0  APPEND ACCESS TO TOPS-10 FILES

TOPS-10 FAL does not support APPEND file access.  If  you  attempt  to
append  to  a  remote file on a TOPS-10, you will receive the "network
operation failed" error.



9.0  VMS JOBS HUNG IN MWAIT STATE

VMS programs using the Task-to-Task routines in particular,  but  also
other VMS programs, may hang in MWAIT state if the BYTLIM quota is not
large enough.  If a program hangs in this state, the program should be
tried again with a larger BYTLIM.

SEE ALSO:  "CLOSING LINKS" (below).

                                                                Page 4


10.0  CLOSING LINKS

When closing task-to-task links, user programs should ALWAYS call  the
DIL  routine  NFCLS (TOPS-10, TOPS-20) or DIT$NFCLS (VAX/VMS) for BOTH
ends of the logical link.   If  the  NFCLS/DIT$NFCLS  routine  is  not
called by both the host and the remote programs, then the link may not
be properly closed and all of the resources may not be released.  This
might not be a problem if the user program immediately stops executing
after closing a link, however in programs that continuously  open  and
close  numerous  links,  if the links are not properly closed with the
NFCLS/DIT$NFCLS routine then the user might run out  of  resources  or
exceed quotas, or on the VAX, get hung in an MWAIT state.

The task-to-task examples in the DIL  manual  are  misleading  because
they do NOT contain NFCLS/DIT$NFCLS routine calls for both ends of the
links, although they SHOULD.

[End of DIL.BWR]