41CL - Shut Off that Auto-Turn Off


Annoyed about the 41CL turning off automatically after about 30 seconds being idle?

Then simply set Flag 44. This flag forces the HP41 to continuous on.

Unfortunately this is not feasible by standard means. Executing FS 44 renders a mere NONEXISTENT because system flags are not in reach of the (standard) user.

One solution would be the use of synthetic code. The PPC ROM offers the command "IF" to invert every kind of flag, regardless whether it is a user or system flag.

For the sole purpose to activate Flag 44, here some MCODE:

08E     N
00F O
013 S
003 C ; Name of the routine: "CSON" (ContinuouS ON)
3B8 READ 14 (d) ; Reads RAM register 14 (d) where the flag configuration resides into CPU register C
10E A=C ALL ; Transfers the flag settings to CPU register A
04E C=0 ALL ; Fills CPU register C with zeros
21C R=2 ; Sets the pointer to Nybble 2
210 LD @R 8 ; Puts "8" at Nybble 2 resulting in CPU register C containing a mask where only Flag 44 is set
370 C=C OR A ; An "or" statement cares about the original flag setting being preserved while Flag 44 is set
3A8 WRIT 14(d) ; The modified flag setting is written back to RAM register 14

Now Flag 44 is set and the calculator does not turn off automatically. To get back to the original status simply turn off the HP41 manually: Flag 44 will be not set at the next turn on.

Now some remarks to disclaim any kind of liability here: While the 41CL is on battery power it makes of course sense that the machine is turned off automatically while being idle because the power consumption would eat the charge pretty fast. If you have an external power solution or if you don't care about battery life then the continuous power on is not that critical.


Isn't this what the ON command does?

- Pauli


Isn't this what the ON command does?

Oh, sh..!

I was thinking hard about some way to overcome the auto-turn off and wondered if there was a simple way.

And of course, you are completely right! The "ON" command!

To get kind out off this and regain back a minimum of reputation I would like to state that the code may serve as an example how to manipulate flags in MCODE.

Sorry about this! I made a fool of myself.


Not at all, the more people getting into MCODE the better - it's all an opportunity to learn.

There are several available functions to set/clear/toggle the status of any of the 55 flags: SFX, CFX, TOGF.... have a look at the CCD, CCD_OS/X, AMC_OS/X, etc.


I agree, the more people who try MCODE the better!

One has to start somewhere, and simple routines are a great stating point. Your example has the advantage over 'ON' of being programmable.


I don't have a 41 anymore, but on my 42 'ON' is a programmable command. I assume it is on the 41 also.


No Gerson, it is not assignable nor programmable (manual)



You're right! I should have tried it on V41. Thanks for the link to the manual.



It is assignable. I just tried it and you can assign 'ON'.




You're right Marwan! It's the ON key that is not assignable.


Yes. Unlike the HP48 series where you can assign to any key you cannot assign to the top 4 keys (ON, USER, PRGM, and ALPHA) on the 41.




probably apparent from the above postings but two separate "ON" definitions are discussed:

The "ON/USER" key which under normal circumstances is not
assignable. However on the CX this toggle key and the PRGM/ALPHA
key are reassigned in ED mode. I think I remember that synthetics
may be able to access those key locations.

The "ON" function whose sole purpose is to overide the timed out
"OFF" function by toggling flag 44. This flag, when not set, turns
the calculator 'off' after 10 minutes. When set, the calculator
stays 'on' indefinitely (battery dependent) until selected off
with the toggle switch. I cannot remember if it is set
to 'off' at each toggle 'off' cycle.

Cheers, Geoff

Edited: 21 Dec 2011, 4:06 p.m.


But why is your CL shutting down after 30"?
Mine doesn't...



Nor does mine after I finally finished the lower screw post repair by waiting long enough (23 hours) for the epoxy to cure fully! I followed aj04062's procedure described in his HP-41 Permanent broken Post Fix posting. Because drilling out the 41CL's mounting holes would cause damage, I used an 11/64" square nose end mill bit to remove the plastic posts, then sized two 2-56 threaded standoffs to a bit below 11/64" outside diameter and cut to length. Two 2-56 binding head screws completed the repair.

Edited: 20 Dec 2011, 7:11 p.m.


This really astounds me. I thought it is a feature of the 41CL but instead it evolves to be a bug although insignificant?

With my 41CL specimen, the shut-off time appears to be independend from the TURBO state and is well below 1 minute. A usual HP41 would shut-off after 10 minutes.

Is there any entry point where this time can be manipulated?


Try going through these advices first.



This may be due to the early display driver chips. Take a look at this thread to determine the display driver type and the solution if in fact this is the source of the problem:


If the display drivers are covered with little caps like show in this example, rather than epoxy blobs, then you'll need to add the capacitor as shown here.

Edited: 21 Dec 2011, 11:24 a.m.


If the display drivers are covered with little caps like show in this example, rather than epoxy blobs, then you'll need to add the capacitor as shown here.

By adding a capacitor the issue with the auto-power off within 1 minute in idle state has been resolved.

Thank you, Monte!

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