HP+.DOC
                           -------
                  Documentation for HP+.COM
               Version 1.0  (c) Eric Meyer 9/84


Did you ever wonder what A00h/32 was, while editing source code?

     HP+.COM is a special version of my programmer's calculator
program HP.COM, which allows the calculator to remain installed in
RAM, always available for use, even within another program!

     The plain calculator program HP.COM will run on any CP/M 2 or 3
system.  It operates much like a Hewlett-Packard RPN calculator, but
has four display modes (bases).  See HP.DOC for instructions on how
to use the calculator.  This file describes only the peculiar features
of the RAM-based version, HP+.

     HP+.COM will ONLY work under CP/M Plus (3).  When installed,
it occupies 2.5K of RAM just under the BDOS.  Do not install it more
than once, or more RAM will be wasted.  It can be called up for use
at any time, until you do a cold boot (reset).  It has "continuous
memory" - if you exit and return to HP+, the stack and memories will
remain unchanged.  If you no longer need HP+ and wish to recover the
memory it occupies, it can be removed from RAM.

     TO INSTALL THE CALCULATOR:       A>HP+

     TO REMOVE THE CALCULATOR:        A>HP+ OFF

     TO USE THE CALCULATOR:           Type control-caret (^^).

(Note: if nothing happens immediately, follow the ^^ with RETURN.)
The HP+ calculator should then appear on the line where your cursor
was.  Use the calculator according to the instructions in HP.DOC.
When you're done, type a ^C to exit HP+.

     When you exit, HP+ returns you to EXACTLY where you were in the
program you were running, which is still expecting input from you.
The HP+ numeric display remains on your screen, but your program doesn't
know that, so it doesn't matter.  In an ordinary text editor, for example,
it will be replaced by the text that's "really" there as soon as you start
moving the cursor around.

                  USING HP+ WITH UNUSUAL SOFTWARE

     HP+ will work as advertised above either from the CP/M "A>" prompt,
or from within any program that does ordinary output to the screen, and
ordinary input through a BDOS call (including BIOS calls through BDOS 50).

     HP+ may operate unexpectedly in programs that use memory-mapped
video.  For example, using HP+ from within the VDO-EX text editor on my
Osborne Executive, the calculator appears at the bottom of the screen
regardless of "cursor" position; and upon leaving HP+, that line may there-
after appear in underlined video mode.  However, these cosmetic differences
do not interfere with use of the calculator, or normal editing.

     The only real problem is that HP+ will simply NOT work from programs
that do input through direct BIOS calls.  Now, there is NO excuse for
software intended to be used under CP/M Plus to be written this way, but
someone may have been sloppy.  (My bundled Wordstar had this problem.)
You may also be using software originally intended for CP/M 2.  In any
case, if you have some assembly language skills, you may be able to patch
the offending program to work with HP+.  You must replace any direct BIOS
CONIN calls with a jump to a patch that sets up a BDOS 6 direct input
call.  Your program's operation should remain the same, but HP+ will
now work in it.

     For example, here is the patch I had to install in my Wordstar 3.3.
It has a routine 16DE that does direct BIOS calls by fetching the WMBOOT
address from Page Zero.  I found this by searching for LHLD 0001, which
occurred at 1D75, followed by CALL 1777, MOV A,C, PCHL.  When this is
called for input, there is a 6 in A, which the subroutine at 1777 adds
to WMBOOT, giving CONIN.  So I changed CALL 1777 to CALL 02EB (a location
in the MORPAT patch area), and at 02EB I put the following code:  CPI 6,
JNZ 1777, POP H, MVI C,6, MVI E,FD, JMP 0005.  Thus the other BIOS calls
continue undisturbed, but the jump to CONIN is replaced by one to BDOS 6.
Afterwards, HP+ functioned perfectly from within Wordstar.