MLDL2000 Specification Update


I have just uploaded the official version 1.0 of the MLDL2000 Specification. Those who are interested are free to download the PDF file from
In the past I have had questions for other formats, but I am trying to keep the spec under revision control, so PDF is what you get.

Progress: The new state machine works, I seem to have just a tiny little bug in the address decoder, which I hope to fix tonight. If this works the next steps are:

- Make USB I/O work, this is actually more software work than hardware, but not extremely complicated.
- Get the PCB routed and make real proto's!

Overall expectations: put the MLDL2000 on your Xmas shopping list ;)

To avoid flames: this is NOT a commercial project, I will sell units at cost. Unless of course HP has the common sense to start producing the HP41 again (or anything else that has I/O ports. I will be first in line to hook up something to it).



Overall expectations: put the MLDL2000 on your Xmas shopping list ;)

Well done Meindert!!!

Sign me in for a couple of them, thanks :-)



I think I might wet myself.

Do I understand correctly that this will give me a way to protect the precious investment I have in rare HP-41 modules by copying their ROM images to the MLDL2000? An giving me access to them all (well some) of them at the same time?

Put me on the list for one.

Oh, the dream of learning m-code is within my grasp.

Mark Hardman


At cost?? Wow - you are a generous person, Meindert!
All the time and effort put into this, and all you ask
is your own out-of-pocket...
Please put me down for one as well. I am VERY much looking forward to 41 ML!!


I know sometimes I'm dense but what in the world is a "MLDL2000"?



From the MLDL2000 Specifications:

What is an HP41 MLDL?
MLDL stand for Machine Language Development Lab. Sounds cool and high-tech, doesn’t it? But what does it? The HP41 architecture understands two programming languages: User Code and Machine Code (or M-Code). The latter is normally not available to end-users. Expansion of the HP41 system is usually done with plug-in modules, or ROM (for Read Only Memory). These contain either User Code or M-code (or a mix thereof). These ROMs could be produced by HP only, although larger groups (like the PPC who made the famous PPC ROM) could develop code and have it produced by HP. When details of the HP41 interface became known it was apparent that the ROM could actually be emulated by (battery backed) RAM. An unused HP41 instruction was defined by the user community to enable writing into the RAM and the Machine Language Development Lab was born. It was now possible for end-users to write and test their own M-Code and later burn it into an EPROM.

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