CASIO fx-3900P memory increasing (with keystrokes) is possible?

[rprosperi]

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?