HP41 ROM Modules


Dear all, I have a question regarding the expansion ROM modules for my 41s:

I own both an HP41CV and a CX.

I also have a module that is labeld 'X MEMORY' (HP82181A). If I recall correctly, that module will give the CV both the memory and functions of the CX (bar the Time/Date functions). I would like to know if that is correct, and also if there is no use to keep that module in my CX (extra memory maybe?)

Also I have a module 'HP-41 Advantage' (HP 5061-7285). This seems to add functions not present on eiter CV or CX.

The same goes for 'CCD MODULE' (82500B-E66 ID 9/11 USA) I presume.

Thanks for your insights!




your X-Memory module is just that: memory (238 registers;-)
To access the x-memory space, you need some mamnagement functions which are in another module called X-Functions.
This module has 124 RAM registers, too.

Your 41CX has the X-Functions module and it's additional 124 registers built-in.
Your 41CV doesn't. So if you want to use the X-Memory module in your 41CV, you first have to install an X-Functions module.

Some things to notice:
You can use up to 2 X-Memory modules at the same time in the same machine.
If you put one of these into port 1, the other one can't be put into port 3.

If you put one of these into port 2, the other one can't be put into port 4.

Any other combination is allowed.
This restriction is due to address conflict reasons.

For the Advantage Pac:
This one adds some functions to the system, and many matrix functionalities. These matrix functions were taken out of the CCD module where they originate.
So you shouldn't use them both at the same time.

The CCD module has many features, like system and user interface extensions, port and HP-IL catalogues,
the mentioned matrix functions, printing, ....,
and much more.
IMHO the CCD module is the best ROM module ever made for the HP-41 series.
The only module which offers more features is the HEPAX;-)

Hope this helps.





I just wanted to mention a couple of things to add/clarify to the above excellent explanation.

You can use the X Memory module on a CX (up to two modules) and they will add extended memory.

I have the manuals for the Advantage, X Memory, and X functions pacs (but not CCD), which may be also available on the Museup CD-ROM, so let me know if you have any other questions.

Best regards,

Ion Abraham
Albuquerque, New Mexico


I have the CCD Module manual in English and in German.


I mean absolutely no disrespect, but I notice that you are putting "(New Mexico)" after your name. I believe the convention here is to put the name of your country there and as is often the case, no mention is assumed to mean the United States.

I only bring this up because both of my parents are from New Mexico and I lived there till I was 14 and I know it is a source of consternation and entertainment that people outside of New Mexico often don't realize it is one of the United States. You might know the column in the New Mexico Magazine titled "One Of Our Fifty Is Missing" where people tell their experiences such as being asked for their passports when they are traveling in the United States and say they are from New Mexico. My parents went through that when they moved to New York in the 1940s.

But since the reason for naming your location is so others from your region, who might have some knowledge or requirements in common with you, will be aware of your relationship, I'm sure there's no reason why people shouldn't name their state.

I live in Texas and like all ex-patriate New Mexicans, I miss the chile.


Dear Ellis,

Yes, the reason I started naming the state was because
of the reasons stated in your third paragraph. At one
point, I don't recall when, someone posted that it would
be nice if people indicated their location, so that others
might form groups more easily. So I thought that was a good
idea. I will, however, add USA after it from now on.

I have occasionally heard of people thinking New Mexico
was a foreign country, but I didn't take that too seriously.
You've convinced me otherwise. I am a recent arrival to
Albuquerque, New Mexico, and so I'm still adjusting.

I'd be glad to send you some chile.

Best regards,



Thanks for the offer. Relatives send red chile and we sometimes bring back a bag of green chile when we visit. What you miss most is green chile being available at any hamburger joint!


The HP-41 is a 64K computer, whick provides for 16 pages of 4K ROM, and has a machine language instruction set (mcode) that does permit bank switching wherein it is possible to have an "extra" 4K that is toggled between. This technique was first used in the HP-41 Advantage (HP 5061-7285) (The HP-41 Advantage is a 12K ROM).


F Port 4, Upper 4 K

E Port 4, Lower 4 K

D Port 3, Upper 4 K

C Port 3, Lower 4 K

B Port 2, Upper 4 K

A Port 2, Lower 4 K

9 Port 1, Upper 4 K

8 Port 1, Lower 4 K

7 HP-IL Mass Storage ROM

6 Printer ROM

5 TIMER ROM; [Secondary Bank] Extended Fuctions (41CX Only)

4 Diagnostic Module

3 Extended Functions (41CX Only)

2 Operating System

1 Operating System

0 Operating System

All of the above addressing refers to ROM, or in the case of a RAM BOX or HEPAX Module with RAM, memory that is sometimes called quasiROM . [

The RAM is treated differently, and has seven bytes per address, 8bits per byte. In an HP-41 sixteen registers are dedicated to suystem registers. On the HP-41CV, HP-41CX or and HP-41C with quad mememory module, there are 320 registers available to allocate between PROGRAM memory and DATA REGISTER memory. This allocation is accomplished by the SIZE command (or also PSIZE on the HP-41CX or with the Extended Functions Memory Mod HP82180A on the HP-41C or HP-41CV ).

The Extended Functions/Memory Module (EFM), HP 82180A adds 868 bytes more memory for your HP-41C or HP-41CV in what is termed Extended Memory and also adds many new functions. Assuming you have the HP 82180A installed on an HP-41C or HP-41 CV OR you have an HP-41CX:
you may install one or two Extended Memory Module HP 82181A to add 238 registers (1,666 bytes) to the available EXTENDED MEMORY, for a maximum 600 registers of Extended Memory.

The HP 82181A can not be used (it just does not do anything) without either:
1. an HP-41CX
2. (on the 41 C or CV) an HP 82180A

Note: The Extended Functions/Memory Module (EFM) HP 82180A can not be used on the HP-41CX because it is already built-in as noted above at Page 3 and 5 of memory. {nl]
The reference to Page of memory in a 64 Kilobyte computer comes from hexadecimal numbering. The lowest address is hex 0000 and the greatest address is hex FFFF . The left-most digit wouyld be the greatest, and would be the Page Number


There is almost nothing else to add to all excellent explanations given here, but I have one small point to add.

In no way an HP41C or CV will update to an HP41CX, even when any of them - C or CV - is added both Time Functions and Extended Functions/Memory. I have seen a post on Classified Ads claiming that an HP41C or CV would be transformed to a 41CX by adding an X-Functions. Some operating resources AND functions are exclusive to the HP41CX and are not available on a 41C/CV nor in both modules. These operating resources and new functions are explained in Appendix H (if I am not wrong), HP41CX Manual - Second part.



Very true (and annoying) that a C/CV will never be identical to a CX despite ROM additions. The new additions to the CX are described in Appendix I of the CX manual Vol 2.

For instance, catalogs 4, 5, and 6 of the CX are not
available on the C/CV.

Oh well,

Ion Abraham
Albuquerque, New Mexico



if you have a CCD module you 'll have those catalogs on the C/CV, too, and even more;-)
You then have CAT 0 through F...



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