The Museum of HP Calculators

HP Forum Archive 08

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Modules for HP41
Message #1 Posted by Luis Sisamon on 17 June 2002, 12:29 a.m.

Hi, I hope this is not a very obvious and dumb question. I was wondering if it is possible to dump the HP41 modules into a hex file and dowload it to the HP41 using any method (optic wand, serial transfer...) More generally, would it be possible to maufacture the modules as they seem to be scarcer than the calculators themselves. Given that HP is no longer active in this field, it should be reasonably esay to reach some form of agreement to solve the intellectual property aspect. Any views?

Re: Modules for HP41
Message #2 Posted by Chris Catotti (Florida) on 17 June 2002, 7:33 a.m.,
in response to message #1 by Luis Sisamon

The HP-41 HEPAX Module by VM Electronics had ROM and a RAM (Maximum 16 K RAM) that allowed you to copy ROM's to mass storage (tape, disk) or to HEPAX RAM from a module or from mass storage. This could then be run as a pseudo-ROM. So yes ir can be done as was circa 1985.

Re: Modules for HP41
Message #3 Posted by Vassilis Prevelakis on 18 June 2002, 5:48 a.m.,
in response to message #2 by Chris Catotti (Florida)

Chris Catotti (Florida) wrote:
> So yes ir can be done as was circa 1985. 

and in 1969 we could send men to the moon. Can we do it now? NO.

So the question is not what could be done 17 years ago, but what can be done now. From pictures of the device it looks like there are two chips mounted on the module carrier, one that contained the EPROM and another that handled the communications between the EPROM and the HP-41 bus.

Doing the same thing today will probably be so expensive so as to be impractical. Thats why HEPAX modules sell for hundreds of dollars.

However, if portability is not a consideration, there are low cost solutions available today (e.g. the MLDL project described elsewhere in the archives) that allow you to download ROMs and run them as if they were modules.


Re: Modules for HP41
Message #4 Posted by Ellis Easley on 18 June 2002, 8:57 a.m.,
in response to message #3 by Vassilis Prevelakis

The new MLDL project is based on a microcomputer that handles the HP41 serial memory interface and has RAM connected to its parallel bus, IIRC. If you could find a micro with fewer pins (no parallel memory expansion bus - I know they make them) and so a smaller package, and which has a large enough internal (EP- or EEP-)ROM to contain the serial interface and houskeeping code as well as the HP code, you might be able to fit it on a small PCB that would fit inside a 41 module or inside the 41.

A micro running fast enough to emulate the 41 serial memory interface might draw a lot of current, and it would have to stay powered up whenever the 41 is on, to monitor the interface so as to recognize when it is being addresssed.

An FPGA could monitor the interface with less power, and its gates could be used to make a ROM, but I've never heard of a PLD with lots of gates that didn't have a proportionally large number of I/O pins (and a big package).

Maybe a small PLD could be used to monitor the 41 interface and then address an 8 pin serial EEPROM. Such a PLD would have to have a relatively large number of "buried registers" - flip-flops whose outputs don't have I/O lines dedicated to them - to keep the pin count low, because you need a number of flip-flops to build a shift register to hold the address for comparison, and some more flip-flops to build a counter or state machine to control the EEPROM.

Re: Modules for HP41
Message #5 Posted by Meindert Kuipers on 19 June 2002, 7:57 a.m.,
in response to message #4 by Ellis Easley

I am working on an FPGA based MLDL. The current specs are available my own site at I just haven't found the time to complete the project, not to publish the VHDL descriptions that I have as of now. Doing a very basic MLDL in FPGA is not very difficult, but some of the functionality the I want to add is a bit more tricky. Power consumption is a potential issue. I would suggest to take Warren Furlow's excellent V41 emulator as a start. I does work as an MLDL (although it is not mentioned in any of the docs as far as I know, the WROM, hex 040 is implemented), with the right module. I managed to have the David Assembler working on it. Now just wait for the real thing. VHDL specialists are welcome to take part in the project.

BTW, I have just found some old docs (including the David Assem manual) that I intend to scan and put online.


Re: Modules for HP41
Message #6 Posted by Ellis Easley on 19 June 2002, 12:30 p.m.,
in response to message #5 by Meindert Kuipers

I have been searching the Forum Archives this morning and I realize I have mixed up bits and pieces of earlier discussions, including your project and John Ioannidis's project using a PIC. Off the top of your head, is there a small package PLD (maybe 28 pins or less) that has enough internal registers to do the 41C interface and address a serial EEPROM for a ROM only implimentation (EEPROM programmed externally)? This addresses the idea of producing new modules (assuming one has the rights to the code inside!)

Re: Modules for HP41
Message #7 Posted by Meindert Kuipers on 19 June 2002, 2:59 p.m.,
in response to message #6 by Ellis Easley

The serial EEPROM is something that will probably work with a small PLD or FPGA. It is just that the decoding needs quite a few registers. I will look into this. The next thing is how to get the code into the EEPROM. Most obvious is through a PC interface, but that is complicated enough with my FPGA. I am open to further ideas ...


Re: Modules for HP41
Message #8 Posted by Ellis Easley on 19 June 2002, 5:02 p.m.,
in response to message #7 by Meindert Kuipers

I haven't actually done it, but I have read data sheets for serial EEPROMS and I have seen circuits incorporating them. As I understand it, they have a clock line, a data in line and a data out line. You clock commands into the data in line, then either clock data in or out through the appropriate line. As I recall, the only critical timing on write is that you have to make sure power doesn't go away for a few miliseconds. This idea of building new ROM modules would allow programming to be done only once, maybe through another conector.

I'm sure there are complications. I just looked on the Microchip website and downloaded some app notes and data sheets. I saw parts up to 512K bits. Ideally, they would contain 10 bit words and each word would be individually addressable. In reality they are available with 8 or 16 bit words. While the small ones (1K bit) might be word-addressable, it looks like the bigger ones are organized in pages. Does the 41C have a Ready line? It might be that the address isn't available early enough to clock it in, along with the command info, so the output data is available when it needs to be.

I'll do some reading and let you know what I find. I'll study the EEPROM timing and get more familiar with the 41C timing.

Re: Modules for HP41
Message #9 Posted by David Smith on 18 June 2002, 6:35 p.m.,
in response to message #1 by Luis Sisamon

From my records of around 40 readers about 50% of all readers are "CARD READER". The other 50% are equally split among "1E", "1F", and "1G" versions. I have never seen or heard of a any B,C,D, or H+ versions.

Re: Modules for HP41
Message #10 Posted by John Ioannidis on 20 June 2002, 1:28 p.m.,
in response to message #1 by Luis Sisamon

Even though I have built my own ROM emulator ((still) preliminary web page at, the only pleasure I derived from it was actually building it!

I wonder what other people here would actually do with the ability to download arbitrary code into a module-sized unit. Is anyone here really using their HP41 for anything other than sentimental reasons? I hope the answer is "yes", but I can't think of one.

Re: Modules for HP41
Message #11 Posted by Ellis Easley on 21 June 2002, 8:31 a.m.,
in response to message #10 by John Ioannidis

I think the beginning of this thread was the somewhat mercenary idea of producing new copies of rare modules. The question of rights has been set aside for the moment! But if such a programmable module was available, it could also be used for new programs. Also, can't user code be stored in ROM modules? People could put their important programs in modules for safekeeping. (Of course, a popular topic here is how to make 41's forget!) Or if not for safekeeping, then for installing new programs more quickly (and easily, in the field) than from card, tape, or disk - even if it is just for sentimental purposes!

For my part, I always prefer broken things to brand-new working ones because (1) I love having an excuse to open things up and (2) I get a lot more enjoyment from trying to fix things, or figure out how they work, than I do from using them.

Re: Modules for HP41
Message #12 Posted by Luis Sisamon on 2 July 2002, 11:24 a.m.,
in response to message #11 by Ellis Easley

First, thank for all the answers. I think now I have a better understanding of what I do not know 8-)

Maybe my first question should be if there is any difference between the contents of a module and a user program. If not it should be possible to load the module contents (card reader, serial-HP-IL, wand,...) in the RAM memory. Or, if if there is any reasonable posibility of manufacturing modules, you could use them to store libraries of routines. I think, this in fact should have been my first question.

Regarding property issues, I thought HP has donated this ROM contents some time after discontinuing the HP41 series, maybe I am wrong (correct me if this is the case).

Finally, regarding the mercenary idea, I do not think this would be very profitable. High prices are commanded by collectors and I do not believe people would pay "collector" prices for items that can be produced today... maybe I am wrong people can be weird sometimes.

Certainly there could be a certain market for producing modules for some of the hobbysts here. I would be happy to be able use a customised module service if available, and probably there is more people like me who would enjoy their machines more if they had this option.

I think this could somehow compensate the people who are working on this; the money they could make would certainly not compensate their skills, time and effort but could be certainly a sweetener (this would depend on the incremental cost of producing a module being not so high).

Re: Modules for HP41
Message #13 Posted by Bill Smith on 21 June 2002, 1:31 p.m.,
in response to message #10 by John Ioannidis

actually, i still use my HP41 to run a couple of lengthy Users Library programs that i'm too busy/lazy to adapt to a faster platform.

i have successfully run one of the ~1000 line programs using the Calc41 software emulator on the HP200LX. someday, i'll figure out why the other won't. until then, it's not a museum piece.


Re: Modules for HP41
Message #14 Posted by Mike (Stgt) on 2 July 2002, 12:19 p.m.,
in response to message #13 by Bill Smith

There are 3 (me and 2 others) I know who run HP-41 code on the 200LX using JF Ganiers emu41. But what is Calc41? Could you pls show an URL?



Re: Modules for HP41
Message #15 Posted by Bill Smith on 3 July 2002, 6:50 p.m.,
in response to message #14 by Mike (Stgt)

Calc41 was produced by Tacit Logic Systems, of Beaverton?? Oregon. They also produced Trans41 for file transfers and translations (see the Articles on Leo Duran User Code and related issues).

I think TLS is out of business. I bought a copy from EduCalc about 1986, and it may be V2 or 3. It runs on DOS, and in general does very well on the 200LX. Most programs copied using Trans41 run flawlessly. One nice feature is the PC can simulate a printer. I never had one until a couple years ago when i bought a used 2225B along with the 82973A PC adapter. There were several User's Library programs I remember having to modify extensively to run without a printer.

I have my 100LX here at work, but don't have Calc41 on it, so don't know off the top of my head that it works; but it should. I'll check over the weekend.

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