someone who has the 4mb ram card working properly

[hpmin48gx]

(02-05-2023 01:35 PM)Christoph Giesselink Wrote:  

(02-04-2023 05:29 PM)hpmin48gx Wrote:  Well, what I have tried does not have that error, that is why I would like to send one, rather that invalid card error according to the card manual appears when you block the write mode

Many years ago I tried to fix the card problem with a ROM patch in Emu48.

The first problem, when you try to access the last bank in the 4MB RAM, the chip enable signal for the RAM get lost. This is an issue caused by a special behavior of the bank switcher hardware. This can be fixed by a ROM patch.

2nd, after fixing the bank switcher problem, I still got errors. The 4MB card is divided into 32 bank of 128KB. For each of these banks the OS reserve some in the calculator RAM in a table for administrative purpose. I was very astonished when I recognized that HP developers made a calculation mistake. The reserved table space had not room for 32 entries, only for 31! So the last entry in the table shares the memory with other intermediate data. So when the intermediate data was written, the administrative bank data for the last bank get lost. The corrupt data is then detected when you switch on the calculator. This cannot be fixed by an easy ROM patch.

So there's definitely no chance to get a 4MB RAM card properly working in a HP48GX.

Hello Sr. Christoph, the only thing I want is to know if the copy of the card works the same, whether it's good or bad, I could send you one if you allow it.
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