HP 48G upgrade - 4mb info


I was just wondering if anyone has any more info on upgrading the hp 48 to 4mb. I know there is a document in hp.org about it (by Philippe TEUWEN) but it is very short and does not have much details. I was hoping to get some info that basically tells one what to do. If anyone has further info, that would be great. Thanks
(Does anyone know of someone who has actually done it?)

Edited: 17 Nov 2005, 8:03 p.m.


I did a 128k upgrade myself years ago, had a bit of a problem getting the case back together. I bought a 48g upgraded to 1 MB from Cynox, they did a great job, and it's performed superbly ever since. I don't know if they still do the procedure, but it's worth checking out.


I upgraded a 48G to 128k and had planned to add an additional 512K later (never bothered as I then got a 48GX and bought a 128K and 1 meg card from Koltz). Physically the chips I looked at would have to be piggy backed stacked to get me to the RAM I wanted (I wanted 1 meg and only found 512K ram at that time). I suspect you might be in a similar prediciment (only with 1 meg RAM, I don't believe I have ever seen a 4 Meg SRAM of the type needed for the 48 series). It isn't easy for the surface mount variety to extend their pins to piggyback. (of course I am getting older and can't see all that well anymore either).

However, I did consider a 2 meg (I didn't really consider the 4 meg card) card. I still have used less than half of the 1 Meg.

If you do succeed in adding the 4 meg, 256K (and maybe as much as 512K) of it will be on no real use to you. The memory is partitioned out in ports with port 0 and port 1 unavailable to your 4 meg of RAM (thats the first 256K of RAM that the 48G uses). And the 48G uses RAM in 128K increments (so 4 Meg would be 32 ports). That is a lot of ports to keep track of. Koltz uses bank switching and a switch to swap the last two ports for his 4 Meg cards.

I find my 1 Meg is fine for my use and I can understand someone even wanting 2 Meg. 4 Meg on the 48G's memory scheme is probably just for some exotic applications that you are very unlikely to need.

Of course if you can find a way to just land a 1 meg chip on the location of the 128K ram location and get the circuity to work with a few jumpers (you will also need a couple of other components as well) to get the 48G to use anything above 128/256K (may be able to merge the next 128K w/o the extra circuity, but I wouldn't bet on it.


I don't really have a need for it at the moment. I just have some spare time on my hands and thought it would be interesting to do. I think that even 1 or 2 meg would be great too - but so far I don't have the info on how to do that either. Are there any takers out there on how to upgrade to 1 or 2 mb? I recently changed the 32k with 128k and will piggy back another 128k on top of that shortly (Opening it was easier than I thought - basically with no damage thanks to some info on hpcalc.org), and am hoping to add another 512 after that (and as I said - even go beyond that.


That first 128K is really easy, just remove the 32K and drop on a 128K chip.

Gets more difficult after that. You also need a low power 7400 chip to tie onto one of the pins (there is a spot on the board for it, not supplied on the Hp48G) and a resister.

More and better information is on hpcalc.org and look/search for RAM upgrades. Photo's are also available. Good luck.

One thing I would consider (if I were you). Buy a card slot (the one supplied for the 48GX if you can find one). Solder it on the board, then solder on the 7400(might be a7404, the info you find will be more specific as this was 3-4 years ago for me). Once you have the card slot, you could by a RAM card from Klotz for $40 that you leave in (wrap it so it wont ground/short out). You would have to cut up your back case to make the card fit, but if your 48G ever failed, you could move the same card over to another ready and willing 48G (or if you ever found a 48GX reasonably). Pulling it out would only result in your 48G going back to its onboard RAM.


Yeah that does sound like a good idea...just have to keep an eye out for the card slot (maybe on a broken gx??). I wonder if they can be bought as a spare part somewhere? Until then, I'll see how I go with the internal RAM upgrade.


Can anyone comment on exactly which 128k memory chips they used? 3.3 or 5v? speed? Power consumption?



I just got 'Hynix HY628100B (LLG-55)' which is made by Hyundai and it works just fine. It was the easiest one for me to get here in Australia (it ultimately shipped from Thailand though) - purchased through futurlec.com. It is very low (LL) power and only 55 ns, which is great. Can download the datasheet for it's specs off any datasheet website.

Edited: 19 Nov 2005, 7:04 a.m.

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