HP-41 Memory chips info (for those HW guys out there :-)


Hi all,

As a collateral effect from other HW activities I ended up with a detailed list of the different memory chips (ROM & D/S) used in the HP-41 "coconut" series.

Many of you will propably know such details, but just in case it may be interesting to someone else, here you can find it.

All the best.


PS. Please let me know if you find any error.

Edited: 24 Mar 2012, 7:05 p.m.


Hola Diego.


Many thanks, my friend. I have to test some boards here and I was only afraid of mixing the ROM versions and had to map them while testing. You have already done what I would be doing ASAP.

Have no idea of how much this info helped me!


Luiz (Brazil)


Hi, Diego, guys;

1) have you ever tried to access the 1LH706/707 with an external X-Fucntions ROM, I mean, would a CLONIX-family or MLDL2000 loaded with a X-Functions ROM image 'see' this first slice of X-Memory? Without this first part, no X-Memory function work.

2) The 1LH701/705 RAM set is found in the HP41CX only? I have not seen them in any CV so far.


Luiz (Brazil)


Hi Luiz,


I'm very happy to have saved some of your time and effort.

To your first question, I have never tried. However just a couple of considerations.

As you probably know, D/S registers "RAM" are not "memory" but a "peripheral" from NUT processor point of view. See this previous thread for details.

So when it comes to handle such peripheral, the Module in charge must not only deal with the typical ROM functions (i.e. be "readable") but also handle and execute a bunch of commands itself (I know quite well since I have to build the decoder for these instructions when developing the double X-Memory emulation for NoV-64 and Clonix-D).

In short, if the instruction handling is implemented into the D/S chip (this will be my guess), it should work with any ROM emulation device (Clonix, MLDL, NoV's, etc). Otherwise it won't work.

However, these chips are (AFAIK) only mounted into CX's so the X-Functions ROM should be there. Shouldn't they?

Anyhow, please share the result of your experiments.

To the second point, I agree. I have only found LH701-5 into CX, however, they could also be used to replace defective D/S chips in a CV. There shouldn't be any functional difference between both kind of chips.

Cheers from Caribean Sea.


Edited: 24 Mar 2012, 8:43 p.m.

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