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What is this "ADV HEPAX module for the HP-41?
Message #1 Posted by Dan Grelinger on 10 June 1999, 9:21 p.m.

I picked up the following module a few weeks ago. "ADV HEPAX". It appears to have a logo "WM Electronics", and a date code of 25-88. Most of the functions appear to be equivalent to the HP-41 Extended Memory functions, and there appears to be memory included in the module. Some of the functions (e.g. HEPAX) I cannot figure out. Does anyone have any info? Thanks.

Re: What is this "ADV HEPAX module for the HP-41?
Message #2 Posted by Chris Catotti on 14 June 1999, 12:26 p.m.,
in response to message #1 by Dan Grelinger

Somewhere I have an advertisement from them, but for now let me retype part of EduCALC Catalog #38, from 1988, page 17:

"HEPAX Modules VM Electronics

Big RAM memory for your HP-41 -- each model of Hepax is a standard-size module containing 8K or 16K of RAM. You can store your own programs and/or data in it and use it just like an HP Application Module.

Two models of Hepax contain, along with their RAM, a 16K ROM full of support functions (including equivalents to all the file-handling functions of the Extended Functions Module). Advanced functions include a powerful tool for disassembling HP-41 machie language, a hexadecimal editor so you can write your own functions in machine language, and a way to transfer whole 4K blocks of Hepax memory to/from mass storage.

'Memory lost' cannot affect your Hepax Module and programs in it can be write-protected -- data is maintained as long as the module is in your instrument.

Comes with a 100p manual. You can use 2 Hepaxs at once, and only one will need the ROM functions.

Stock #41-895A [Hepax, ROM, & 8K RAM] .... $287.00

Stock #41-895B [Hepax, ROM, & 16K RAM] ... $394.00

Stock #41-895C [Hepax, 8K RAM only] ...... $235.00

Stock #41-895D [Hepax, 16K RAM only] ...... $326.00"

Re: What is this "ADV HEPAX module for the HP-41?
Message #3 Posted by Dan Grelinger on 14 June 1999, 7:02 p.m.,
in response to message #2 by Chris Catotti

Chris, thanks very much for the info!

Now, if I can just get a copy of that manual! I have figured out that I have the 16K RAM version with the ROM. It is interesting because the ROM takes up only 4K of address space, (must be bank switched), and maps itself into unused ROM address space, including the printer ROM page, if it is available. I have never seen a self mapping HP-41 ROM before.

Re: What is this "ADV HEPAX module for the HP-41?
Message #4 Posted by Chris Ctotti on 17 June 1999, 5:25 p.m.,
in response to message #3 by Dan Grelinger

From "HPX Exchange", V1N3 (May/June 1987) page 26:

"The EPROM, while being 16K in size, is bank switched ... It has four 4K banks, with the accompanying previously unused Mcode instructions ENBANK3 (140) and ENBANK4 (1C0). The EPROM automatically addresses itself to the lowest unused 4K ROM page starting at ROM page 5. The REMAP ROM instruction (030) ia another new opcode."

Re: What is this "ADV HEPAX module for the HP-41?
Message #5 Posted by Dan Grelinger on 17 June 1999, 8:43 p.m.,
in response to message #4 by Chris Ctotti

This is truly an amazing device. If the inventor of this piece is still around, I would like to congratulate him on his great work. Alas, since there does not seem to be many of these around, he must not have sold many.

For the auto ROM addressing to work properly, the ROM must default at turn on to an address that is definitely not used. This would either be page 4 (reserved for diagnostic, and executed only at machine turn on), or in the address corresponding to the port the module was plugged into. I have a way of checking this.....

Wow, I did not know that ENBANK3 (140) and ENBANK4 (1C0) instructions existed. This means that 32K ROM modules were possible in each port of address space. A programming nightmare, but possible. Theoretically, a 128K ROM (or RAM) module could be made that logically occupied all 32K of port addressed ROM space, and banked switched 4 times as much memory using the bank enable functions.

I have confirmed that the memory is lost immediately if the module is removed. One interesting feature of this module is that it stores programs and data very similarly to the Extended Functions Module, with one major difference. When a program is saved, it automatically becomes a Catalog 2 program, executable. This is something that is not done in the EFM. Another major difference is that when used as data registers, the 16K of ram converts to 2610 registers, a healthy number.

Thanks for the information Chris, you are a scholar and a gentleman. (Assuming that Chris is used in the masculine sense, of course).

By the way, is the HPExchange article you mention on either the Museum CD, or another one?

Re: What is this "ADV HEPAX module for the HP-41?
Message #6 Posted by Chris (Christopher) Catotti on 18 June 1999, 12:50 p.m.,
in response to message #5 by Dan Grelinger

Information on the CD-ROMs of PPC Journals, PPC ROM Manual, ZHPX Exchange and more, all in Adobe PDF can be found at

This is an invaluable reference. The name HEPAX dervives from HEwlett-Packard 41 EXpansion (use the capitalized letters).

On the thought of additional RAM [see HPX Exchange V1N2 page 20] "Four diffent HEPAX modules. The module comes in four versions:

- A standard HEPAX module containing 8K of RAM and all the above support functions and many others.

- An Advanced HEPAX module containing 16K of RAM and support functions as above.

- A HEPAX Memory module contatining an additional 8K of RAM without any built-in functions.

- A Double HEPAX Memory module containing an additional 16K of RAM ithout any built-in functions"

from page 21 ...

"The RAM resides in the address space reserved for each port. In the case of a double module, it occupies the address space of the port and its neighbour and thus must be mounted beside a system addressed device or an empty port. System addressed devices include the HP-41C Memory module, The Extended Memory, Time and HP-IL modules and the HP82143 Printer"

Re: What is this "ADV HEPAX module for the HP-41?
Message #7 Posted by Dan Grelinger on 18 June 1999, 11:06 p.m.,
in response to message #6 by Chris (Christopher) Catotti

Yeah, I have the ADV HEPAX version, and figured out the fact that the RAM occupied two ports worth of address space real quick. The ROM version is "-HEPAX 1C"; I wonder if that was the latest version.

I guessed that HEwlett PAckard eXtension was where they got the name. Just for grins, I searched the web for HEPAX, and only came up with medical references.

Besides the Extended Function equivalent functions, which I have figured out, there are these, some of which I do not have a clue how to make work;

PRIVATE - makes a stored program, private CLRAM - kind of obvious, but it wants some input I have not figured out CODE - probably similar to the ZENROM function of the same name COPYROM - wants an input. I severely locked up the -41 trying to figure it out. DECODE - see CODE above DECODXY - see CODE above DISASM - This is cool, it dissassembles code to the display, and I assume to a printer if connected. HEPAX - Don't have the foggiest. HEPAXA - Probably like HEPAX, only uses the Alpha register HEXEDIT - Probably a RAM/ROM editor. HPROMPT - No idea RAMTOG - No idea READROM - HP-IL function to read rom image to QRAM WRTROM - Equivalent to READROM above XF - No idea XFA - XF using alpha?

Re: What is this "ADV HEPAX module for the HP-41?
Message #8 Posted by Mike on 24 June 1999, 6:07 p.m.,
in response to message #7 by Dan Grelinger

As I know there is a version 1B, 1C, and 1D. All not working yet in my Nut-Emulator on the IBM mainframe (But SERVICE 1C does!) Ciao

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