HP-75 RAM expansion?

[Martin Hepperle]

(10-13-2016 10:38 AM)Michael Fehlhammer Wrote:  Hmm, I don't understand all these hardware intricacies, but a general question:
I thought 24 kB is the maximum RAM an HP 75 can address due to limitations of the address space.
Could more RAM be managed by the operating system (without patching it)? Wouldn't a complex bank switching mechanism have to be implemented?

Michael,

yes, the directly accessible RAM memory of the HP-75 is indeed limited to 24K.

Only with some "tricks" additional RAM could be switched into the ROM window as ROM replacement. The Pod and PDS seem to be examples of such applications.

The background of my inquiry:
I have a rather battered up sample of an HP-75 without the RAM module and I wanted to see whether it would be possible to add the missing RAM without locating another original RAM module for $$$.

In fact, after reading said article (or was it a nightmare while I slept?) I bought six (4+2 just-in-case) TOSHIBA TC5516AP 2048x8 BIT CMOS Static RAMs and now I cannot locate the article anymore...
And yes, it were FOUR chips to add, not TWO... my mistake.

On the other hand, if someone would design a PRM-75 similar to the PRM-85 for the HP Series 80 machines or even a FRAM-75 that would be something even more interesting...

Martin