HP41CY - Replacing the internal +3v lithium cell

Dear HP41CY enthusiasts,

have a look to the HP-Museum article folder about replacing the internal +3V lithium cell of the HP41CY....

Regards - Christoph Klug



thank you much for this great article! Unfortunately, it seems that the OS of my RAMBOX is already damaged; not totally lost, but not working properly anymore. In your article, you say, that reloading the OS is a complex procedure. Can you give us an outline of this process? Which tools are needed?

Thank you,


Maybe the simlest way is to have the RamBox OS in a Clonix module. I think it should be possible to copy it from there to the Rambox without problems (or is the copy protection still working in the Clonix)?
I will try this with my next CY with dead OS.



Hi Matthias,

I will try this as soon as I have my CLONIX programming adaptor. I have a 32K RAMBOX, and your module list shows two different versions. Does anyone know the difference between the 1B and 3M versions? Which one should I use in the case I cannot determine the version of my RAMBOX?

Matthias, can you provide me the ROM images of both 32K RAMBOX versions?

Thank you,


Dear HP41 RAM-Box enthusiasts,

it seems to be easy to reload the operating system of non bankswitched RAM-box systems = 32KByte RAM-Box systems. I done this several times : In this case you are able to install an ERAMCO os to an W&W RAM-Box or a W&W os to an ERAMCO RAM-Box, depending which os you prefer or which os size you like to store inside your RAM-box (4KByte or 8KByte). In any case this solution will work.

First you have to clear the RAM pages of the RAM-box, for example by using the ZENROM. When the HP41 is able to switch on correctly including the RAM-Box, the clear process is finished. For reloading you only need the CCD-D from Raymond, stored inside an ZEPROM or Clonix. Use the commands SAVERAM and GETRAM and store the needed os to IL-CASS-Drive. Than switch the internal protect switch of the RAM-Box to the write position, and save the os to the RAM-Box page. Now place the switch back to the protect position.
For W&W RAM-Box solutions place the os to page 8, for ERAMCO RAM-Box solutions place the os to page E + F = 14 + 15.

Much more complex is the os reload process of bankswitched RAM-Box systems which includes 64KByte = two banks (W&W and ERAMCO) or 128KByte = four banks (ERAMCO). For this systems we are looking for a working solution....

Best regards - Christoph Klug


Has anyone tried to run the RAMBOX funtionality on the MLDL2000? It does support bankswitching, and loading images is not too difficult.

Just curious,




thank you much for clarifying the procedure! Having a 32K RAM-Box only seems to have at least one advantage ;-)

I'm still wondering what the difference is between the 1B and the 3M version of the 32K RAM-Box (see Matthias' module list). Is 3M just an update to 1B? Any idea?

Best regards,

Juergen Keller


Dear Meindert,

does your MLDL2000 really include the bankswitching mode needed for RAM-Box applications ? A RAM-Box switches between full 32KByte pages (not 4KByte pages).

As I know the bank switching from W&W is different to the bank switching of ERAMCO. Jean-Francois Garnier have knowledge about this, because he implement both RAM-Box solutions to his great EMU41 emulator software...

Regards - Christoph Klug


This would be interesting. Right now only traditional bankswitching is supported, meaning that a BS instruction switches an 8K page (both upper and lower pages of a module port). If our friend Jean Francois is following this thread, could he explain the RAMBOX switching in some detail?




Dear Meindert,

I think it would be a great extension for your MLDL2000 system to include the bank switching solution needed for RAM-Box applications.

From W&W exist the 64KByte RAM-Box version - that means two 32Kbyte pages are bank switched. From ERAMCO exist 64KByte and 128KByte RSU (RAM Storage Unit) versions - that means two or four 32KByte pages available. Furthermore I heard rumors about a 256KByte RSU version from ERTAMCO (but I never hold this in my hands) - that means eight 32KByte pages are available.

I will close the contact to Jean-Francois Garnier, for transfering some bank switching knowledge from EMU41 to MLDL2000 :-)

Best wishes - Christoph Klug


Hello Meindert,

Just to refresh your memory, you can have a look
here :-)

At the request of Christoph, I also implemented the 4x32kb=128kb ERAMCO Rambox (to be available soon in next Emu41 release). The bank switching is even weird, using no ENBANK opcodes at all...

Kind regards.



Hi, I actually stored the rambox os from my CY away onto the PC via the MLDL2000 and then was able to load it back onto the calc on another page (so that I had two there, just for checking). I have not tried to use the os on the MLDL on a normal cx without a rambox, but I'm not sure what use it would be, other than looking at modules plugged and the like. Not sure if that was the question, but I tried anyway...



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