Old HP48SX resurection and upgrade

[manjo]

Hello all,
I had an old 48SX (revE) in a drawer for a long time.
when cleaning my drawers I found 128k*8 SRAM low power chips
in one of my other drawers, so...

For fun I thought to upgrade it to 128k.
Upgrade went fine, desoldered the built in 32k very clean an nicely

I put in 128k top 4 pins remained without pads (unconected)
bridged Vcc pin to CE2 (this is VCC) and routed A15 and A16 to
pins 18 and 19 on expansion connector (A15 and A16 respectively)

Everything works fine, only... MEM still reports 30k :-(

Is IRAM fixed size in ROM on 48SX (revE)?
Is it not A15 and A16 pins 18 and 19 on SX?
Other Thoughts ideas ?

[Claudio L.]

(02-16-2019 07:38 PM)manjo Wrote:  Hello all,
I had an old 48SX (revE) in a drawer for a long time.
when cleaning my drawers I found 128k*8 SRAM low power chips
in one of my other drawers, so...

For fun I thought to upgrade it to 128k.
Upgrade went fine, desoldered the built in 32k very clean an nicely

I put in 128k top 4 pins remained without pads (unconected)
bridged Vcc pin to CE2 (this is VCC) and routed A15 and A16 to
pins 18 and 19 on expansion connector (A15 and A16 respectively)

Everything works fine, only... MEM still reports 30k :-(

Is IRAM fixed size in ROM on 48SX (revE)?
Is it not A15 and A16 pins 18 and 19 on SX?
Other Thoughts ideas ?

Welcome back!
I have no idea if it's fixed in ROM but if you connected the address lines, it should be visible to the CPU, my first instinct would be to try some peek and poke from Saturn assembly to see if the RAM is there or not.

[mfleming]

There are upgrade instructions at hpcalc.org. Try checking your work against them to see if you missed something. Here's a link to one description

https://www.hpcalc.org/details/5440

~Mark

[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

[rprosperi]

Keep in mind that if you wire the additional RAM as Port-1, you can then merge that 'Port RAM' into main RAM, achieving the same basic thing as your original goal, assuming you don't plan to use Port-1 for a real card.

[manjo]

(02-19-2019 02:12 PM)rprosperi Wrote:  Keep in mind that if you wire the additional RAM as Port-1, you can then merge that 'Port RAM' into main RAM, achieving the same basic thing as your original goal, assuming you don't plan to use Port-1 for a real card.

As a matter of fact I wired it to pins closer to RAM and ROM chip, it turned out that those are PORT2, PORT2 MERGED with IRAM as expected:
2 MERGE
and that's it...

Interesting thing is that, in some places ports are refered to as Port-0 and Port-1, on other places PORT1 and PORT2...go figure...
It seams .. I was just lucky...

[rprosperi]

(02-19-2019 05:14 PM)manjo Wrote:  Interesting thing is that, in some places ports are refered to as Port-0 and Port-1, on other places PORT1 and PORT2...go figure...
It seams .. I was just lucky...

Port-0 is not the same as Port-1. Port-0 is a section of Main RAM that has been set aside for storing Libraries. So if you STO a library file using :0 as the storage location, a portion of Main RAM is allocated (and removed from Main RAM) to store that object.

So on the SX there really are 3 areas for storing libraries, Port-0, Port-1 and Port-2. On the SX, Port-1 and Port-2 can only hold 128KB HP RAM cards, while on the GX, Port-2 can hold larger cards, accessed in 128KB virtual 'Ports' (i.e. Port-3, Port-4... Port-33 for a 4MB card); internally, these virtual ports are transparently mapped into the same address space as Port-2 via a bank-switching scheme, collectively called 'Covered Ports', but addressed by the user as Port-3, Port-4, etc.

There also were 256KB and 512KB RAM cards for the SX made by Tripod Data Systems, which were similar to the GX covered ports except the user had to manually use commands to select which port was active (only one at at a time could be accessed, but you could program card selection to make it somewhat automatic); these were always addressed by the physical port number that the card is in. Although these cards do not say 48SX on the label, they can be identified by the combination of RAM size (256 or 512) and copyright date before the GX was introduced in 1993. All the cards of this type I've seen have copyright date of 1991, though I imagine '90 and '92 are feasible as well).