

                        4DOS Critical Error Handler
                                Version 2.00
                                 Revision B
     
WHAT IS IN THIS FILE ?

     This file includes a quick overview over 4DOS24H2 and a quick instal-
     lation manual.  It also includes an overview of the files included in
     the archive, some technical information together with bugfixes and
     changes in this version/revision.  You are encouraged to read all of
     this file before installing 4DOS24H2.COM - it will take a few minutes.
     If you face problems you can turn to the section dealing with trouble
     shooting in the manual.


WHAT IS IT ?

     4D24H20B.ZIP contains a new critical error handler designed to replace
     the one present in the otherwise excellent 4DOS command interpreter
     from JP Software. (The normal critical error handler is the piece of
     code printing the notorious message 'Abort, Retry, Ignore ...' when
     you have forgotten to close the drive door to the diskette drive - it
     also called an interrupt 24h handler).  It is inspired by 4DOS24H from
     Patrick Philippot but completely rewritten and optimized in almost any
     possible way.


WHY USE IT ?

     4DOS24H2 writes much more comprehensive information in a pop-up window
     and accepts more flexible user input than does the original handler.
     It saves and restores the user screen and is able to utilize enhanced
     text modes, e.g. screen mode 22h (44 rows by 132 columns) on Tseng
     based SuperVGA cards.  It tries to detect graphics modes and acts by
     calling the original 4DOS handler which will activate the speaker.
     Contrary to other external 4DOS critical error handlers (that I am
     aware of) this one is also operational during shells.


QUICK INSTALLATION

     Extract the file 4DOS24H2.COM from 4D24H20B.ZIP to your 4DOS directory
     and put the following line in your existing 4START.BTM file (or create
     one if you have not already got one):

       [d:][path]4DOS24H2.COM

     were 'd:' is your boot drive and 'path' is the path to the directory
     were you keep 4DOS24H2.COM.  If you are running an appropriate memory
     manager or DOS version 5.x or later you can also load the handler high
     by using the proper command (for DOS 5.x it would be LOADHIGH).

     Reboot your computer to make the handler take effect.


WHAT'S IN THE 4D24H20B.ZIP ARCHIVE ?

     The archive includes (besides this README file) a documentation file,
     two assembled versions of the handler and the source code.  The two
     assembled versions are identical except for the number of columns in
     their pop-windows -- 4DOS24H1.COM uses 40 columns while 4DOS24H2.COM
     uses 41.  The last one is generally the nicest but cannot handle the
     old 40 column screen modes, so if you use a 40 column screen mode
     regularly you should consider using 4DOS24H1.COM.


TECHNICAL DETAILS

     The handler is written in assembler for maximum efficiency (source
     code is included) and uses only 2448 bytes of memory (4DOS24H2.COM).
     It can be loaded high using 4DOS 4.0 or later and an appropriate
     memory manager (e.g. DOS 5.0 or QEMM).


CHANGES IN REVISION B FROM INITIAL RELEASE

     A BUG-FIX

     If you switched on the printer echo facility by pressing Ctrl-P and
     your printer was off-line you would inevitable end up in a deadlock
     when pressing <Enter> the first time.  If you had a printer you would
     have to switch it on-line to return from the handler.  If you had no
     printer at all the only salvation was to press Ctrl-Alt-Del.

     This was not a special feature of 4DOS24H2 as the built-in handler in
     4DOS behaves the same way (at least in version 4.01).

     In this revision you can press Ctrl-P to switch off echoing to the
     printer before pressing 'a' to abort the operation.  As a minor
     curiosity you will have to press 'a' twice to abort.  This is not a
     bug in 4DOS24H2 but due to the way the printer echoing facility is
     implemented.


     A COMMAND LINE SWITCH

     In this revision a command line switch has been added for debugging
     purposes.  If you append '-M', '/M' or just 'M' the handler will print
     the load address and the exact memory usage when going resident.  The
     gross memory usage is a bit higher than stated by the handler because
     DOS allocates memory in 16 byte chunks.  A bit slack must therefore be
     expected.
