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

NutEm/PC copies the logics of a Nut CPU to interpret the firmware of HP41 and Voyager 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.

Reason for update 9/2/2021:
i) Hit-n-hold of keys, an important control element (e. g. to display program lines when SST) now works if mouse operated,
ii) ON+key gesture, up to now simulated at startup only now achievable by right mouse button and Ctrl key at the same time.
iii) naming changed to NutEm/PC, lengthy 'Nut firmware interpreter' was working title only. It stays an interpreter.

Reason for update 8/8/2021 (unpublished, overtaken):
i) executing TIME CHIP test of service ROM 2A shows "TIME IC  OK" hooray!
ii) CR function VER inserts self-acting multi-track card decks in full  —  after all...
iii) incomplete read decks of data cards (by RDTAX or due to lesser storage as when written) no longer jeopardize subsequent operations,
iv) CR reads from LIF disk dumps now also filetypes 'E050'x (41KEYS) and 'E060'x (41STAT).
Note: Simulation of CR and IR printer module is distributed separately.

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 NutEm on the mainframe it's now NutEm/PC with some enhancements.

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. This NutEm/PC distribution comes with two devices, the Time Module and the HP-82143A printer (w/o graphic). Enough to play a bit. Card Reader and "Blinky" IR printer module are included in a separate bundle without source code.


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 re-program 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.

Today the 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 do something 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.
Note: 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.

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

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:

About The ROMs

The used ROM format is "user readable", 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 (see also snippet further down).

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.
Here 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,
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,
41's beeper someway imitates the role model only but at least you are warned when typing the 24th character in alpha,
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),
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,
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).
All known bugs are fixed, at least two remain unknown: one inserted invalid code in a user program what made the complete RAM file useless. Another one filed RAM incomplete. Up to now those two errors showed once only.

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 trace logs, nothing else.

Manuals of the role models

HP-41CV Owner's Handbook and Programming Guide,
HP-41CX Quick Reference Guide
HP-10C, HP-11C, HP-12C, HP-15C, and HP-16C.
In case you like to know more there is a torrent about almost all HP41.

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:


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.

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