VAX BASED
			 CP/M 'MODEM7' COMPATIBLE
			  FILE TRANSFER PROGRAMS


    This  document describes the file transfer system in use between a
    VAX 780 and an IBM PC.  This file transfer  system  is  compatible
    with the CP/M MODEM7 file transfer protocols, and was developed in
    C using the public domain CMODEM program as the basis for the file
    transfer portion.  

    Two  filter  programs are provided in the package to insert/delete
    CR's in CR/LF combinations to match the VAX  conventions  on  text
    files.   These  routines  are  run  on  the  VAX,  and are invoked
    automatically by the use of the appropriate DCL procedures.  These
    DCL procedures should be used on text files only.  FTP  should  be
    used directly when transferring binary files.

    The programs in use are as follows:

	$ FTP -x FileName

	This routine handles file sending ('-s'), receiving ('-r'), or
        appending  ('-a')  from a remote system.  Direction of flow in
        the above commands is relative to the  VAX.   On  the  command
        line  -x  is  one  of the above (-s,-r,-a) and FileName is the
        file to be sent or received.

	$ VAX2IBM InFile OutFile
	
	Routine  to  convert LF-only line termination to the CRLF line
        termination required by CP/M and MS/DOS compatible systems.

	$ IBM2VAX InFile OutFile

	Routine to convert CRLF line termination into the LF-only line
        termination required by the VAX RMS file system.  Also removes
        any CTRL-Z characters found (CP/M EOF marker).

    The DCL procedures in use are as follows:

	$ FSEND FileName

	Invokes  VAX2IBM to build a properly formatted text file, then
        FTP to send that file to the remote system.

	$ FRECV FileName
	
	Invokes  FTP  to  receive  a text file from the remote system,
        then invokes IBM2VAX to properly format that file for VAX RMS.

    A couple of notes are in order:

    The  FTP  routine is set up such that only ONE port is required in
    order to run it, the terminal that issues the FTP command  is  the
    same  one  that  sends/receives  the  file.   The  use of a simple
    terminal emulator program to activate  the  VAX  is  all  that  is
    required.   The  protocols  are  set  up  for this form of delayed
    synchronization.  FTP has been tested at 9600 baud and should  not
    fall  behind.  When the VAX is heavily loaded, occasional timeouts
    may occur.  These  timeouts  most  often  manifest  themselves  in
    checksum  or  other errors.  The timeouts are necessary for proper
    synch of the protocol in case of errors, and may not be disturbed.

    DEC  C  runtime will output the LF's to the file during the IBM to
    VAX conversion.  This differs  slightly  from  the  way  it  would
    appear  on  the VAX in RMS native form (null characters, with some
    form of char count as termination).  If file is then copied  using
    the  DCL  COPY  command, the LF's are removed, and Null characters
    and char counts are inserted in their place.  The  only  places  I
    have  found  where  the  conversion format will cause a problem is
    with the DIFF command, and with CMS.

    With  DIFF,  use DIFF/IGNORE=SPACING to cause a comparison of file
    contents only.  With CMS, edit the file  and  save  it.   The  new
    version will be in the correct format.

    The  original  MODEM  program  was  developed  by Ward Christensen
    several years ago, and has undergone  extensive  modifications  in
    the  user  interface.   The  protocol  has  not changed, except in
    spin-off versions that play around  with  CRC  instead  of  simple
    checksums  for  verification.   These  are  normally identified as
    MODEM9 and and above.  

    There  may  be  other (possibly better) protocols around, but this
    one has become the de facto standard for the micro world.  If  you
    have  problems,  contact me before changing the protocol.  I could
    actually have an implementation bug (shock!).  It has  been tested
    fairly extensively with at least two other  systems, but bugs  are
    insidious.

    Bugs,  enhancements  and  any  other wild ideas should be reported
    via mail to LOAFMAN (TCC01 or TCC02), or via phone to:

        Kenneth W. Loafman
        work: (214)556-8889 (sometime during the day)
        home: (214)245-2618 (before 10:00pm weekdays)