HP41 system ROM related - versions and compatibility


Hi, all HP41 addicted!

After causing many (very good) reactions after bringing the ROM-images subject up, I would like to know about the many HP41 system ROM versions and their compatibilities. Most of the discussion lies on the coconut, because the halfnut series do not allow 'mixing' the system ROM´s as they are not accessible separately. I confess I did not research the Forum archives, but I actually do not remember reading about this specific subject.

The system ROM versions I'm aware of (thanks to W. Furlow) are:

ROM 0   1   2
Each system ROM is stored in one single chip (coconut series), so they could possibly be mixed with each other. My questions to those who have already dealt with these ROM´s are:

- what are the valid combinations?

- which of them are specifically for the CX?

- which, if any, can be used with either the C/CV and the CX?

This would depend both in observing actual configurations or in official documentation. I have some 41C/CV I could check for a few samples, and also three CX, but these would be just a few samples. The possible combinations are in vaster number than the actual working combinations, so I decided to ask.

Thanks again!

Luiz (Brazil)


Is there a command that will return this information?


REVX? will return the appriorate info;-)

Actually the revision is at the end of each system ROM page.




Not in a command available at the basic system ROM (C/CV or CX). Ángel´s Toolbox has OSREV? command, and as Raymond mentioned, HEPAX, David Assembler and many other specialized ROM offer editors and viewers that allow inspecting the ROM addresses with this information (xFFB to xFFE, x being the block # from 0h to Fh).


Luiz (Brazil)

Edited: 30 Nov 2009, 11:06 a.m.


Thanks Luiz and Raymond.


FYI, the Service ROMs All have the ROM command (press the [-] key).

Per above discussion, the later editions of "Extend your HP 41" that Wlodek wrote has all of this information already captured in nice list format. (See the table of contents on the Version 7 DVD)

Also, on the latest 41CX rom, there are 2 sets of ROM characters: NFL and DCC.




Combinations other than these probably won't work properly. When versions of two of the ROMs changed at the same time (FDE->GFF, and GFF->NFL to produce the CX), there were patches that included jumps from one ROM to another.


Hi, Eric;

thanks for your (so necessary) answer. I found an HFF version set in a halfnut. Will any of these combinations be found in one of the both types and not in the other (coconut and halfnut)?

One extra question. Although it leads to a logical conclusion, chances are that the answer is 'NO': is the CX 'F-version' ROM1 the same CV 'F-version' ROM1? I mean, do these carry the same code and are interchangeable?

Cheers and thanks again.

Luiz (Brazil)


The halfnut was only manufactured with the final ROM revision for each model (HFF, NFL). I haven't seen HFF in a non-halfnut, but it may have existed. The vast majority of 41C and 41CV units have GFF or HFF.

I'm moderately certain that mainframe ROM 1F contains the same code in the C/CV and CX.

Note that the CX mainframe has a total of 24K of ROM using two 1LG9 chips. Beyond the hard-addressed "mainframe" ROM, there are three more 4K ROM blocks in pages 3 and 5, for the CX time and extended functions. The CX mainframe ROM won't work correctly without these.

What is it that you're trying to do?


Hi, Eric;

I am almost sure you were around here when I posted this message (long time ago... that HP15C is still working fine!). I actually have some related ideas because I have two 41 MBoards behaving strangely and I would like to mix their ROM IC´s so I could test one with each other´s. But I needed to know what was I doing prior to go ahead mixing ROM´s without coherent information. These babes beep, show garbage and freeze randomly. Sometimes they accept one or other key, then I loose them again.

I tried their RAM chips in other coconuts, and they work fine. Then I tested their capacitors (value) and diodes, and they are also fine. Now I would like to identify their ROM and try changing one with the other. In fact, I have a 41 MBoard with connectors for all RAM and ROM (six 8-pin DIL) so I can build a 41C anytime and test RAM and ROM chips. RAM chips are easy to test, but for testing ROM chips I needed this kind of information.

Now the last part of info is: IC's ID# for each version, so I can test them accordingly.


Luiz (Brazil)

Edited: 30 Nov 2009, 11:16 p.m.


Now the last part of info is: IC's ID# for each version, so I can test them accordingly.

I've found very little information on part number vs. ROM ID. Some is on this page. I'd certainly like to add more (and corrected) information.


Hi, Eric;

I'll do the following, then: take notes of whatever I find and, if there is anything not in your indeed very complete and comprehensive lists, I´ll post again and let you know. This is the least I MUST do to thank you for your support 8^)

Best regards.

Luiz (Brazil)


Hi, Eric;

I was building a document with the information you passed us and found that ROM1-E.ROM does not appear in any of the possible combinations. Do you know if this ROM is used in any particular model?


Luiz (Brazil)

Edited: 2 Dec 2009, 11:23 a.m.


Which would the purpose of this topic?
Can we change ROM's of HP41 or that is only a waste of time or Luiz would be building a super HP41LV to give a present us in Christmas? :-)

Edited: 1 Dec 2009, 10:52 a.m.


For sure.

I searched the archives to see if this kind of subject was previously mentioned amongst others or not, so I decided to bring it up mostly to shed some vintage subjects in the air. Good to see that calculators like the HP97 and other vintage ones are still in use and serving people well. They also call for follow-ups.

I am sure that some people found purpose in this topic.


Edited: 1 Dec 2009, 5:32 p.m.

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