HP-48GX RAM Cards - Better with or without built-in battery?


Dear Forum members,

I've only recently installed Raymonds Speed UI on my HP-48GX (brilliant piece(s) of software by the way, Raymond!). However, since it blocks my 128k RAM card in Port 1 almost completely, I'm considering to go looking for a new RAM card maybe with 512k or even 1MB.

Apart from the fact that they are quite expensive I'm a bit cautios about the TDS and SMI cards with the built in battery, especially when they were stored for longer periods without power supply (as will mostly be the case for the cards sold on TAS I guess). I fear tht the NiCd battery in the cards might be at the end of its useful life after a long time without a single charge.

What is, in your opinion, the better choice:
1.) Buy a TDS/SMI card with built in battery and "risking" it dies early or,

2.) buy a smaller (and somewhat slightly cheaper) 128k card with exchangeble battery?

I'd really appreciate your feedback on this.

Thanks a lot in advance and best regards,

Edited: 13 Feb 2011, 9:52 a.m.


You have mail:-)

Best Regards



I'd definitely go with one that has a replaceable battery. There's no telling what kind of shape those old rechargeable ones would be in, and replacing the cells probably isn't easy.

I'm pretty sure you can find cards larger than 128KB that use replaceable coin cells. Of course, like any large cards, you won't be able to MERGE them, and the cost of obtaining them will be about equivalent to several arms and legs.


I have a related question. Is there a spec available for the RAM slots on the 48GX? Would it be possible to build myself a RAM card?

I'm looking to put to a CAS on my 48GX but the 128kb of internal RAM doesn't leave me with enough free space for other purposes. I'm not willing to pay $300 for that though (I could buy 3 50G's for that price -- two to replace the others when the keys start sticking).


I've wondered this as well. Has anyone ever researched if a SRAM card could be modified to fit in the slot of the HP48?

I think you would need the earlier (type 1 or 2) card.


way back people were using memory cards for smith-carona typewriters. however, it was marginal if a given card would work or not - as far as i can recall the smith-corona cards were designed to operate at a slightly higher voltage than the HP ones, and could latch up due to input protection circuitry.

my recollection is that the cards are essentially just an sram chip (62256 or similar) with some glue logic. these days (with surface mount device readily available) it should be quite simple to produce a card with one _large_ sram chip, no glue logic needed, and a switch on the top edge of the card to select from a number of banks. alternative, a cpld could be used to implement calculator-controlled bank switching.

the input protection on the original cards is largely superfluous, especially if a large card is left permanently in the calculator.

addendum: CY62177EV30LL-55ZXI-ND from digikey, us$36.00 in quantities of one. "TSOP I Configurable as 2M x 16 or as 4M x 8 SRAM". this is a package that is hand-solderable, about 2mm high profile, with all the needed address and data lines brought out. 2.2-3.7v operation. with a bit of luck just this device, a soldered battery, 2 diodes and a suitable connector would do the trick, all assembled onto a small pcb. battery drain in standby is 3uA - technology has come a _long_ way in 20 years since the 48 was designed!!

rob :-)

Edited: 14 Feb 2011, 8:44 a.m.


Hello everyone,
I actually bought in Germany a handmade RAM card from an undergraduate student of electronics 10 years ago. I don't want to write one of those emails I really hate to read but... here we go.
I have to look for the card (I pretty much know where it is) in my parent's house so I can get it in two weeks.
If anybody is interested, I can make pictures of the PCB, write down the component's part number and from there make your own RAM card.
I used the card for many years on my HP48GX until I placed in a drawer on my parent's house. So it should be there.
Please advice if you are interested on it, it is a double sided PCB with batery backup.


I found a web page to build 128kb RAM CARD. I think the one I have is the same. The link is below:

Home made 128k Ram Card

Edited: 18 Feb 2011, 4:06 p.m.



Yes, please can you post images of the custom made RAM CARD that you used for years. HD images will provide a look at how the RAM CARD was built.

Let us know if you find it.

Thank you,

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