HP Forums

Full Version: CASIO fx-3900P memory increasing (with keystrokes) is possible?
You're currently viewing a stripped down version of our content. View the full version with proper formatting.
I found this pdf: Calculator programmes (Mr. Francis Hung) with the following interesting last page:

To increase the number of steps of memories in 3900p
(1) Open the case with screw driver
(2) Take out the batteries
(3) Close the case with screw driver without batteries
(4) Press several times “AC”
(5) Open the case with screw driver and then put the batteries into the case
(6) Close the case with screw driver
(7) Turn “on” the calculator and press ‘mode’ + ‘0’
(8) Clear programme 3 and programme 4
(9) In programme 3, enter 150 ‘+’, in programme 4, enter 151 ‘+’
(10) Clear programme 1 and programme 2
(11) If the number of free steps + number of steps in programme 3 and programme 4 > 1200 steps, then the modification of calculator is completed, otherwise, it has to be started over again.
(12) Press ‘Mode’+‘.’, ‘Mode’+‘4’, ‘Mode’+‘9’, ‘Shift’ + ‘AC’, ‘Shift’ + ‘MR’.

Any experience about this method on this or on another calculator?!
Any similar trick for other models (I can imagine my fx-50F with 1200 bytes memory)?

Thanks for any reply!
Interesting. I know many Casio devices don't have an automatic reset routine when you change the batteries, and they just run with whatever garbage is in memory, often showing an absurdly high number of free bytes. The fx-3900P looks like it's from the era where Casios needed a manual press of the reset button after installing batteries. I would be very surprised if this actually increases the amount of usable memory.
I have heard of conceptually similar situations in the past where companies sold a product with differing amounts of RAM in different models, but the h/w actually included the larger amount in both. The 'lower' model is initialized at the factory with some command sequence to limit the apparently available RAM to the lower level, and obscure and difficult to implement commands and h/w steps such as these were used to reset to the higher limit.

I have no memory at all which devices did this, but I do not believe they were Casio, as I was never a Casio owner, and never did much research with them.

Do you know if there was a substantially similar model to this one that had more RAM?
According to the information published in this site:



fx3900p and fx4000p were produced more or less simultaneously, with similar or the same set of functions, and externally they look alike

One remarkable difference is that fx4000p features almost five times the memory of fx3900p.

I suppose the only way to find out whether this procedure actually works is to get a fx3900p and try it.
(01-08-2020 10:39 AM)david sanz Wrote: [ -> ]I suppose the only way to find out whether this procedure actually works is to get a fx3900p and try it.

Big Grin I have one like a new, I will try it and I hope it will not bricked.
BTW: I guess this is a classical "wake-up" feature of CASIOs as Dave wrote in the second post. After a RESET the memory will be 100 steps available as normal.

Reference URL's