Old HP48SX resurection and upgrade

[manjo]

Hello all,

HrastProgrammer shed some light on the subject...
-as it seams SX has internal memory mapped between #70000 and #7FFFF
(address space for 64 kNib)
-at #80000 and #C0000 are expansion ports so...
-the chip must be working but SatrunCPU in SX is not able to access it because it's
"under" PORT memory (overlaped)
128 k would be from #70000 to #B0000, but since PORT1 starts at #80000.. anyway...

So, I guess internal RAM upgrade is worthwhile only for 32 k 48G models...
Eventually one could solder another 128 k chip on top of the internal one and wire CE, OE, and W signals to port pins and make it work like a PORT1 or PORT2 RAM card.

Like so:
Wires and voltage sense resistor:
   

Port2 RAM test:
   

Port2 MERGED to IRAM
   

Even so, it's probably not worth it, maybe for a real HP48 enthusiast,
-but I'm a lot like 50G fanboy so...

So much for this time,
regards,
Mario Lohajner
manjo