HP-41 undocumented features

I know this subject has been done to death but I have never seen anything about these "features" of the HP-41. 1st feature procedure : in alpha register, write anything (1 to 12 char. maximum) in program mode, write a loop (make a slow one, like this exemple) : LBL 'AA GTO 'AA Get out of program mode, position the calculator on LBL 'AA, do XEQ 'PROMPT Now do the following, exactly : press SHIFT (and hold) press CLX (and hold) press ON (and release all) you will see the PRGM indicator light up. Now press CLX. If you have followed the procedure, you should see your alpha string moving from left to right. If you use a faster loop like "LBL 00, GTO 00" or better yet, "LBL A, GTO A", the display will go faster. ----------------------------------------------------------- 2nd feature procedure : in program mode, write the following : LBL 00 TONE 9 GTO 00 get out of program mode and do XEQ 00. Now do the following : press CLX (and hold) press ON At this point, this is touch and go. If you're lucky, your HP-41 should emit a very high-pitch sound, if not, run the program again and again, until you get it. At this point, your HP-41 will make this sound each time you touch a key. You can get rid of this sound by making the calculator beep (using BEEP or TONE). If you turn the calculator off and then on, the sound will still be there. ----------------------------------------------------------- Any of you knew about those? got more "undocumented features"? Hope this helpful for somebody or, at least, fun! Jimmy


If memory helps, a similar effect to your scrolling alpha string may be obtained if, after executing a PROMPT, an error occurs while the IGNORE ERROR FLAG is enabled (so no to stop the program. For instance, a sequence like "String" PROMPT FS25 0 : LBL xx GTO xx will show the effect. I am recalling this "feature" from old memories, since my -41C is waiting for a troubleshooting session, so it is not working...


1. This can be done synthetically by manipulating the MSG (message) flag. The MSG flag determines if the display has a message in it. If not, then in program mode, the calculator shifts the display with each Label executed, because it thinks that the "flying goose" is in the display.

2. The second is more difficult to make happen, but can be done with microcode programming. Essentially, when executing a tone, the HP-41 turns on the speaker, runs a loop, and turns off the speaker. When the CLX and ON are pressed together, a soft reset of the -41 is done, and the calc may not turn the speaker back off. Any processor activity will make the speaker squeal, until the speaker is turned back off with another tone command.


Funny, neither of these worked for me.

I remember the goose replacement from many years back being done with the error ignore flag, but I tried that too, and it didn't work.. yes it did (I used PROMPT instead of AVIEW duh!)

01 lbl"AAA

02 "HI


04 SF 25

05 0

06 /

07 lbl"AA

08 gto"AA

and, of course, to make the new goose fly backwards (or the old goose for that matter) place 10 more lbl instructions between line 7 and 8.

Now, I also remember turning the goose around was a trick... but that was a tad harder


You are right about the AVIEW, of course ! The "backwards goose" had to be set by means of synthetic programming techniques (I do not remember the details), but a strange thing was that such character could not be displayed if it was the only one on the display, so an extra dot or something was mandatory...

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