HP-41CL & NoV(-64): Race condition?


I have on several occasions noticed that the MMU on the 41CL has been reset upon turning the calc on when I have a NoV-64 plugged in.

Sometimes the time has also been reset.

This does not occur when I do not have the NoV module plugged in.

I suspect a race condition.


I assume that you mean the the MMU has been disabled. This will happen if the POR (power-on-reset) function on the CL board detects that the supply voltage has dropped below a certain value, even if transiently. The Time Module has a similar function built-in, although it operates off of a different supply. The one on the CL board itself monitors the 3.3V supply for the RAM and CPLD. I think that the only way that the POR(s) can be triggered is if the supply dips because of a surge in current drawn while the CL (and NoV-64) is powering up. Since it is affecting both the CL board and the Time module, this suggests to me that the problem is with the I/O block that connects the battery pack to the main board. If this current path is not able to carry the power-up current surge the voltages at the PORs might dip enough to trigger them. So I would check for corrosion/oxidation on the I/O block connections to the battery and the main board.



Monte; It is regardless of corrosion (both my CLs does this - and only when the NoV is plugged in. Could it be that since the NoV requires juice, the CL will detect a lack of juice abd disable the MMU?


It may be that there is a current surge on power-up from the NoV that is sufficient to cause the voltage to droop enough to trigger the POR. I suppose that there could also be a transient bus fight between the CL board and the NoV, but the 41CL is designed to force all drivers off until it actually comes out of reset, so I consider this to be unlikely. Does it happen less frequently with new batteries? I am not familiar enough with the NoV design to talk about what kind of current surge there might be.


I have not really noticed any difference with new batteries...


I'm really wandering if there is anyone in this world to use the HP-41 for real work. I use it as a number cruncher because of nostalgia.


Isn't nostalgia real work?

Consider the HP-41 as a Glass Bead Game . Then Ángel Martin should be treated as "Magister Ludi".




Then Ángel Martin should be treated as "Magister Ludi".

That'd be an honor (Hesse, no less!), and certainly gentler than "The Last Mohican" - though I needn't say that's not true, just check the "What's New" section at TOS to see.

Cheers, ÁM


I'm really wandering [sic] if there is anyone in this world to use the HP-41 for real work.
This comes up from time to time. Yes, I use my 41cx every day, because it is functional, not because of any nostalgic value.


Of course I use HP41 system - and now the more powerfully and much faster 41CL for real world applications : More in detail - I run hardware interfacing and measurement applications with I/O-Board and IL2000 Interface System, which means HP-IL is included to my applications :-)

Best regards - Christoph



This comes up from time to time. Yes, I use my 41cx every day, because it is functional, not because of any nostalgic value.

I second that. Twice.


Hi Geir, all,

Late as usual but I'd like to help.

Can you please, mail me with details so I can try to replicate the problem.

Thanks and best wishes.


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