HP-41 - Byte Grabber / Key assign ??


Hi all,

I have a HP-41C since 1982. It was used until late 90´s and i tried programming but never did something with synthetic programming.
Without memory and x-function module i thought i had no chance.
But now i re-activated the 41, got a quad ram, x-function module and a card reader and tried some synthetic programming following the instructions here at MoHPC.

So i used the described byte grabber which leads to my question.
The byte grabber is assigned to the "LN" key.
Because i dont know and couldnt find out about the key mapping structure... how can i assign the grabber to another key, for example the "STO" Key ?

I suppose some of you knowing guys can help me!

Thanks in advance!



Hi, Olaf;

as you can see in Creating a Byte Grabber, step #3, instead of assigning [+] to the [LN] key you assign it to [STO] and go ahead with the following instructions.


Luiz (Brazil)


Hi Luiz,

unfortunately its not that easy.
When i just use another key (STO) to assign the + sign step 12 brings a wrong output "04 3" instead of "04 STO 01".
And if i continue the calculator hamgs when trying the STO key in user mode.
As u can read in the chapter "how the byte grabber works" the sentence before the last says that the 6 A´s you enter are related to the LN key. So you have to put in something else than 6 A´s to program it to a different key.
But i dont know how.

Any idea ?




Hi, Olaf;

I finally found my printed version of Wickes' "Synthetic Programming on the HP41C" and then I see what happens. (Yeap, I have a copy of it in the MoHPC CD/DVD set, but I do not like reading 'on screen' text...)

A bit of history: I remember once when a friend borrowed my HP41 and was completely frightened when taking it back to me because he thought he broke it. He was working with summations and pressed [Sigma-] many times while in USER mode, and the calculator crashed in a way it didn't turn on anymore.

I clearly remember having the Bite Grabber ("byte jumper", at that time) assigned to [Sigma-] instead og the suggested [Sigma+} so I had it in a safer, shifted key. Not any safe as long as USER was on, thought!

I had no difficult changing the Byte Jumper position in the keyboard when following the instructions in Wickes' book, and I wrongly assumed it would be easy as well with the ones found in the MoHPC section. Surely the instructions to create the byte grabber in the MoHPC page are easier and shorter than the ones found in Wickes' book, and I'll look at them closer to see how one can change the key where the byte grabber is assigned to.

A brief comment: IIRC, when assigned to the [Sigma-] the byte jumper forced 'XROM 00,08' to be shown in the display when the [Sigma-] key was held long enough it could show its assignment.

Best regards.

Luiz (Brazil)

Edited: 3 Sept 2006, 10:47 p.m.


Hi Olaf, did this work for you? When I try this, my calculator simply freezes.


No, it didnt work.
My 41 freezes too, but without doing anything it is back after 30 seconds, functioning normally.

Look at my earlier response to Luiz...




The book "Extend Your HP-41" also has the instructions to put it only on the LN key. Maybe someone who knows more about the insides or has the museum CDs can tell us if there's a reason it has to be this way, like that the LN key assignment is always at the very end of the key assignment area in memory.

wilsonmineszdslextremezcom (replace the z's with @ and .)


You need the 'Key Assignment Keycodes' and the 'Quick Reference Card" for synthetic programming to be able to figure out the correct character to use in step 14.

E.g., I've my byte grabber assigned to [ENG].

From the 'Key Assignment Keycodes' I can see that the keycode for [ENG] is '3F'.

Then, in the QRC I look up code 3F and find that it corresponds to '?'.

Finally, I assign '+' to the [ENG] key in step 3, and in step 14 I enter '???????'.

However, I don't think you can assign the byte grabber to any key, e.g. the keycode of [STO] is '23' and in QRC it corresponds to '#'. I guess you can't enter that character into the alpha register.

The keycodes and the QRC you can find over at the other site (not sure if I can link directly from this site).

Look for "Inside the HP-41" and "Synthetic Programming Made Easy " in the Books section.



Thanks for your answer!

I will try it out... maybe not to the STO key... i just want to avoid using the first 2 key rows...

If i am successful i will report it :-)

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