NutEm/PC — A Nut Firmware Interpreter Built On ooREXX/Win

NutEm/PC copies the logics of a Nut CPU to interpret the firmware of all Voyager and HP41 calculator models. It is the PC migration of my ancient NutEm written in FORTRAN running since decades on "real iron" under VM/CMS. Today NutEm/PC may still serve on PCs as a simple toy to test some simulation without need to be compiled, just edit and run.

Reasons for update 12/9/2021:
i) CR shows file types in lists of LIF disk dumps,
ii) CR forces R/O for other than standard card format,
iii) CR quickens handling of long lists by enhanced keyboard control,
iv) coloured display used to indicate blinking ( simple on mainframe terminals).
Note: CR and IR printer module are distributed separately from bare NutEm/PC.
Afore running this program read the QPL public license in section 7.


  1. A Brief Description
  2. Prerequisites, Install and Run it
  3. Connectivity
  4. Controls of This Program
  5. Features, Constraints, Known Bugs
  6. Manuals of The Role Models
  7. The Fine Print

A Brief Description

Once upon a time Hewlett-Packard sold pocket calculators based on a proprietary "Nut" CPU. This CPU worked in famous HP-41C/CV/CX and the "Voyager" series (HP-10C, -11C, -12C, -15C, and -16C). With the time the firmware of these machines leaked out what resulted in emulators, simulations, virtual remakes. The firmware interpreter I publish herewith is a great grandchild of those, and in contrast to my feasibility study NutEm on the mainframe it's now NutEm/PC with several enhancements worth to mention.

The HP41 series is extensible by many plug in ROMs and devices. ROMs add more firmware or additional software or both and run at once in this program. Devices add some special hardware which needs to be simulated to work in a remake. NutEm/PC comes with four devices, the Time Module, the HP-82143A Printer (w/o graphic), the Card Reader and "Blinky" IR Printer Module. The later two are distributed separately.


Once triggered by a contribution in a PPC Journal (from a Grecian author IIRC, pieced in almost unintelligible English so the editor mocked about it, describing – what I assumed to grasp – how to simulate a calculator by rebuilding the limited set of CPU instructions instead of redo the floods of functions from plug-in modules), I programmed about two decades ago (in FORTRAN and on a mainframe) a logical simulation of the Nut CPU. Now I ported it to ooREXX under Windows. The idea is to run the calculators' firmware in an facile to program interpreter that does not need to be compiled only to test a little add-on. So I hope it will be easier to simulate more devices.

For me this hope turned true. In rather short time I was able to add simulations of
i) the HP 82242A Infrared Printer Module (first simulation of it at all I suppose) and
ii) the HP 82104A Card Reader (CR). Like the role model the CR reads magnetic cards from HP-67 and -97 (see "Teenix"), additionally also RAW files from V41 and several file types from LIF disk dumps like 41WALL, 41KEYS, 41STAT, 41PRGM, and 41DATA. (Both devices are published apart from NutEm/PC without source code.)

My goal is not to be a better emulator than the well known but to have a toy that serves as a simple aid for testing. For some time now there exist other quite suitable simulations/emulators/virtual remakes of those HP calculators prolonging their time of use. Nonetheless I publish my NutEm/PC, may be someone else may find it practical too to waste some time with it.

Prerequisites, Install and Run it

To run NutEm/PC you need (in brackets what I used for the development):

To run under NutEm/PC any of the a. m. calculators you do need copies of its firmware (ROM). For your convenience I add following for a first try.

11C and 16C (virtual remakes of 12C and 15C are available from HP in here)
version GFF
HP41 add-on
Time, 82143A printer, The HP-41 Advantage Advanced Solutions Pac, and PPC ROM.
  • I do know this files contain software which could still be protected by copyright. In the hope all authors may be proud to see their work still in use, I enclose it with NutEm/PC. Please see also Acknowledgments in the Advantage manual and PPC ROM documentation.
  • Simulations of CR and IR printer module are distributed separately.

    Install it

    There is no automated installation procedure. Unzip ooNUfip.ZIP to a directory named at will, a directory of its own or not, it's up to you.

    Note: Keep the organization of subdirectories, 'HTML' at least, otherwise you have plenty to trim in the CFG files. If you move 'HTML' or its content you even have to modify the program or hit F1 is of little help.

    First Run and Subsequent Runs

    Open ooNUfip.CFG first using a text-only editor of your choice and if necessary adapt it to your installation. For further explanations see comments therein. In future do this step for modifications only. To have a distinct CFG file for a different model I suggest to file it with a new name you may use as option when starting NutEm/PC.

    NutEm/PC is a console application which displays some information, warnings and trace output only on the console window. "Real" errors will be shown in a dialog in the middle of the screen. If not interested in those informations of minor importance, you may prepare one or several shortcut links which start NutEm/PC to your flavor without console window.

    Start ooNUfip.rx either by

    • open a command window in the directory where you installed NutEm/PC and enter (without quotes) "ooNUfip" or "REXX ooNUfip.rx", it depends on your choice of suffixes at installation of ooREXX,
    • start the windows explorer, navigate to the directory where you installed NutEm/PC and double-klick ooNUfip.rx or right-click it and select open
      (alas drag-n-drop of a CFG file to the REXX program does not work),
    • single-click a shortcut link you prepared before.

    NutEm/PC optionally takes one argument and/or several options (one at a time). More tailoring is done within an CFG file.

           [REXX] ooNUfip[.rx] [CFG-fileID] [ #KEY]
    a file-ID or name of a CFG file ('.CFG' will be appended if missing), default is 'ooNUfip.cfg'.
    Separated by ' #' (blank and "Gartenzaun", garden fence) one single designation representing a key that will be "held down at on time". Meaningful for the Voyagers are one of ',./*-+' (dot or comma to change the decimal separator, dash to get a reset, slash for a keyboard test, the rest for single or endless self-testing). 'BA' (back arrow) induces a complete reset (MEMORY LOST) of HP41. With a PANAME ROM plugged one of '.,AKMTV' are also operatively, see Appendice ON of its manual.

    For subsequent runs you don't need to edit CFG files unless you like to change something.


    NutEm/PC is currently not equipped neither to simulate HP-IL nor to link to Virtual IL. So today there is no need to talk about connectivity.

    Controls of this program

    Keys: F1        - show this help file (if your PC affiliated suffix HTM with a browser),
          F2        - displays the About information,
          F10       - activate menu (HP41 only),
          Shift+F10 - (also Shift+M) activate menu (Voyagers only),
          Ctrl+C    - copy display to clipboard,
          Ctrl+X    - copy X-register full precision clipboard,
          Ctrl+V    - use clipboard content as input (see note 3),
          Backspace = Back Arrow,
          Pause     = Enter,
          End       = R/S,
          Return    - hit the selected button,
          Esc       - ends the program,
          Underscores in the button's caption denote which key will press it (see note 1).
    Buttons: Same as role model.
    System Menu: Underscored letters indicate which key will launch an option
          Quit w/o saving RAM      - ends NutEm/PC keeping RAM of previous session
          Reset Nut cycles counter - zeroes CPU counter
          Show program...          - displays user program (see note 2)
          Copy figure as displayed - copy display to clipboard
          Copy complete X-register - copy X-register full precision clipboard
          Paste number to X-register - use clipboard content as input (note 3)
          More details...          - same as F1
          About...                 - guess what...


    1. The buttons' caption change according the shift status and with it the acceleration keys. On HP41 shift and alpha is relevant, on Voyagers it is f-shift, g-shift, user mode.
    2. This menu item is only available for Voyagers, to list programs on an HP41 use a printer.
    3. The number from clipboard is interpreted to detect thousand's separators, comma, sign and exponent. What may not belong to the figure will be missed silently. This fuzzy logic is not perfect, so use with caution. An HP41 in alpha mode will put it as text to the alpha register, characters will be uppercased. (A ZEN ROM may disturb this process.)
    Mighty Mouse

    Besides the easy handling by keyboard or mouse the later offers two additional options:

    • For the HP41 hit-n-hold is an important element of the man-machine-interface. For most keys (ON is one of the exeptions) keeping a key held down it first shows the function it will execute, and, if still held down for a moment, NULL will be displayed to indicate, you may release the key now with no further action than NULL disappearing.
      The Voyager models offer hit-n-hold for few keys only to allow a prolonged readout, e. g. 'View Mantissa' (Clr Pref) or MEM (storage status).
    • {ON+key} is a gesture for rarely used features like changing the decimal separator on Voyagers or reset HP41 to factory-set. This option is available if the simulated machine is off, if the Ctrl key is held down, with a right mouse click (if reversed 'the other right') to the calculator's button in question. (Paname ROM is respected.)

    About The ROMs

    For a first try this NutEm/PC comes bundled with few ROMs, including a CX enabled to display lower case letters (a pacht from Jean-François Garnier). More to find
    for HP41
    within V41 and here and there, and if still not enough more here;
    for the Voyagers
    here and there, see also on this pen drive.

    NutEm/PC uses ROMs in a "human readable" format as shown above, columns 1..4 address, column 5 blank or a colon, columns 6..8 command, address and command values in hex. If comments follow they may start minimum at colum 10, separated from commands by one or more blanks. So ZEN ROM decoder print-out will do.

    The ROMs that come with NutEm/PC bundle are unchanged for HP41, patched for Voyagers to fix a stack-lift bug in HP-11C and -16C. In addition you may apply a pause patch to get – regardless the speed of your PC – a 1.2 seconds delay for PSE, MEM, and View Mant (by ClrPref). To do so replace the C=C-1 X in the delay loop by 1F0, an invalid opcode. Following an example for the HP11C, similar at different spots for the others.

    original:                   patched:
    0D11 046 C=0    X           0D11 046 C=0    X
    0D12 21C PT=    2           0D12 21C PT=    2
    0D13 210 LC     8           0D13 210 LC     8
    0D14 266 C=C-1  X           0D14 1F0 ** loop patch **
    0D15 3FB JNC    -01 0D14    0D15 3FB JNC    -01 0D14

    The Time Chip Simulation

    The way the TIME CHIP test of service ROM comes to TIME IC OK is a little bamboozlement. With a service ROM 2A in place I do similar reversing like VW and other cars who change motor regulation as soon as they detect to run unter test conditions – what is by far more than just a dirty trick.

    My reasoning is, when executed in a simulation Nut CPU commands all take different period of time due to their complexity and implementation, moreover the simulation runs on a multitasking system with its typical uncertainty. So it is quite impossible to have the simulated time chip in sync with the wall clock time of the host-PC. Consequently I use the virtual Nut CPU as time standard, 64 command cycles (word time) take 1/100th second, no matter how long this lasts. By that the very pernickety service ROM passes all tests and shows TIME IC OK after all. Neither test content nor addresses are stored within the time chip simulation, otherwise I could fake the test entirely by jumping to the wanted result at once.

    Without service ROM, time and date of the host-PC are master, what makes SETIME and SETDATE of virtual HP41 useless.

    Features, Constraints, Known Bugs

    Features worth to mention:
    Hit-n-holdthe important element of the user interface, functional when using the mouse to operate the calculator (if you prefer to handle by key board you probably like it speedy, hence no hit-n-hold at this),
    {ON+key} available by Ctrl + right mouse button,
    key captions changing with shift status,
    fuzzy logic for pasting numbers,
    41's beeper someway imitates the role model only but at least you are warned when typing the 24th character in alpha,
    executing TIME CHIP test of service ROM 2A shows "TIME IC  OK" - hooray!
    Time with SW (stop watch) and alarms — accurate to a fifths of a second (that is the pace maker's watch frequency at idle time),
    HP41 with 82143A printer – translating 'synthetics' to human readable, eg. RCL M in place of RCL [ like the role model,
    Voyager program listings shown with HP41 style mnemonics,
    trace log shows display changes and read values of RDROM what simplifies to locate code sections,
    in trace log POWOFF is shown correctly as two byte command,
    modification of setup with ease using the text editor of your choice.
    Constraints, missing, annoying:
    The surface looks nasty — by design, to make it distinguishably different (nevertheless NutEm/PC is an emulator of the CPU-simulating kind),
    no graphic on 82143A printer — use my oo82162A IL2IR bridge, works best with IL-enabled V41,
    no HP-IL for now — instead use Emu41 or V41,
    NutEm/PC is distinctly faster than the originals — albeit about 1600 times slower than the PC versions from HP (find 12C and 15C with others in this package).
    Not all bugs are fixed, two showed only once and never again, so they could bite once more. Another one bites at fast scrolling (using the mouse wheel) a list of LIF disk dumps. I should implement a throttle to limit new requests for time-consuming evaluation of LIF disks.

    So you are warned, do not use NutEm/PC for serious work, don't even think about it. I programmed it only to get some insight and nice trace logs, nothing else.

    Manuals of the role models

    If no PDF is referenced directly it's a format to read online (download possible).
    HP-41CV Owner's Handbook and Programming Guide
    HP-41CX Quick Reference Guide
    In case you like to know more there is a torrent about almost all HP41.
    HP-10C Owner's Handbook
    HP-11C Owner's Handbook and Problem Solving Guide (PDF, 11 MB)
    HP-12C Financial Calculator User's Guide (PDF, 2.1 MB)
    HP-15C Owner's Handbook (PDF, 6.5 MB)
    HP-16C Computer Scientist Owner's Handbook (PDF, 2 MB)

    The fine print

    (i) Do not use this program.
    (ii) Any damage you cause with this program, intentional or by chance, is a violation of clause (i). Thus all consequences are completely at your own risk.
    (iii) If you manage to improve this program you have to inform me as stipulated in following THE Q PUBLIC LICENSE (QPL).
    (iv) In addition applies the QPL below:

    THE Q PUBLIC LICENSE version 1.0

    Copyright (C) 1999 Trolltech AS, Norway.

    Everyone is permitted to copy and distribute this license document. The intent of this license is to establish freedom to share and change the software regulated by this license under the open source model.

    This license applies to any software containing a notice placed by the copyright holder saying that it may be distributed under the terms of the Q Public License version 1.0. Such software is herein referred to as the Software. This license covers modification and distribution of the Software, use of third-party application programs based on the Software, and development of free software which uses the Software.

    Granted Rights

    1. You are granted the non-exclusive rights set forth in this license provided you agree to and comply with any and all conditions in this license. Whole or partial distribution of the Software, or software items that link with the Software, in any form signifies acceptance of this license.
    2. You may copy and distribute the Software in unmodified form provided that the entire package, including - but not restricted to - copyright, trademark notices and disclaimers, as released by the initial developer of the Software, is distributed.
    3. You may make modifications to the Software and distribute your modifications, in a form that is separate from the Software, such as patches. The following restrictions apply to modifications:
      a. Modifications must not alter or remove any copyright notices in the Software.
      b. When modifications to the Software are released under this license, a non-exclusive royalty-free right is granted to the initial developer of the Software to distribute your modification in future versions of the Software provided such versions remain available under these terms in addition to any other license(s) of the initial developer.
    4. You may distribute machine-executable forms of the Software or machine-executable forms of modified versions of the Software, provided that you meet these restrictions:
      a. You must include this license document in the distribution.
      b. You must ensure that all recipients of the machine-executable forms are also able to receive the complete machine-readable source code to the distributed Software, including all modifications, without any charge beyond the costs of data transfer, and place prominent notices in the distribution explaining this.
      c. You must ensure that all modifications included in the machine-executable forms are available under the terms of this license.
    5. You may use the original or modified versions of the Software to compile, link and run application programs legally developed by you or by others.
    6. You may develop application programs, reusable components and other software items that link with the original or modified versions of the Software. These items, when distributed, are subject to the following requirements:
      a. You must ensure that all recipients of machine-executable forms of these items are also able to receive and use the complete machine-readable source code to the items without any charge beyond the costs of data transfer.
      b. You must explicitly license all recipients of your items to use and re-distribute original and modified versions of the items in both machine-executable and source code forms. The recipients must be able to do so without any charges whatsoever, and they must be able to re-distribute to anyone they choose.
      c. If the items are not available to the general public, and the initial developer of the Software requests a copy of the items, then you must supply one.

    Limitations of Liability

    In no event shall the initial developers or copyright holders be liable for any damages whatsoever, including - but not restricted to - lost revenue or profits or other direct, indirect, special, incidental or consequential damages, even if they have been advised of the possibility of such damages, except to the extent invariable law, if any, provides otherwise.

    No Warranty


    Choice of Law

    This license is governed by the Laws of England (if not yet part of Spanish East Indies)