Casio FX-602P Ram Upgrade looking for srams

[Hiwi]

In the 80ies i upgraded the ram of my FX-602P, i added srams and a DIPswitch to manage 5 blocks of additional 512 programsteps each.

My bankswitching does not work anymore, so i decided to build it new.
But the static rams D444G/C are not available anymore (since 30 years I think).
Is there someone who has this chips laying around? :-)

You can find the description on the net, but it is a poor scan and in German.
I added it to this thread.

Ralf

[akpoff]

(05-04-2023 11:37 AM)Hiwi Wrote:  In the 80ies i upgraded the ram of my FX-602P, i added srams and a DIPswitch to manage 5 blocks of additional 512 programsteps each.

My bankswitching does not work anymore, so i decided to build it new.
But the static rams D444G/C are not available anymore (since 30 years I think).
Is there someone who has this chips laying around? :-)

Hi Ralf,
Great mod! Do you have photos posted anywhere, even if not working? Did the switching work while the calculator was on?

As for the SRAM, reading the BOM it looks like you need 4 x UPD444C and 1 x UPD444G. I got better search results using those numbers. There's a provider in the EU with the 444C chips:

https://www.ebay.com/itm/203922584276

DigiPart has results for both parts, but they're result lists so you have to contact each supplier to get pricing.

https://www.digipart.com/part/UPD444C
https://www.digipart.com/part/UPD444G

Alternatively, is there enough space inside to put a small microcontroller on a board that presents as the necessary circuit? Even a small controller should have enough SRAM to give you several banks. Obviously it's more work since you have to build it and program it, but long-term it might be easier to maintain and find parts.

Cheers,

--Aaron

[blackjetrock]

Quote:Alternatively, is there enough space inside to put a small microcontroller on a board that presents as the necessary circuit? Even a small controller should have enough SRAM to give you several banks. Obviously it's more work since you have to build it and program it, but long-term it might be easier to maintain and find parts.

Cheers,

--Aaron

There's enough room to replace the entire calculator PCB with a different PCB with a
microcontroller on it:

https://www.youtube.com/watch?v=5w6tmykqrYM&t=4s

As the ROM for the 502 or 602 hasn't been dumped yet to my knowledge the code
has to be re-written.

You could probably replace the RAM chip with an RP2040 as here:

https://www.youtube.com/watch?v=XirGbH-HYOA&t=6s

With an RP2040 and similar code to that RAM replacement you could use some of the 260K or so of RAM and even the 2M of flash as storage. An extra SD card could also be added to save the RAM contents.
If the 602 runs at 5V then you might even be able to get away with no level shifters as in the RAM replacement above.
Andrew

[Paul Dale]

Springing for an FX-603P is far easier and less likely to ruin a beautiful calculator.

I really wish I'd kept the book of FX-602P programs I wrote. Some real gems in there.


Pauli

[blackjetrock]

(05-05-2023 05:24 AM)Paul Dale Wrote:  Springing for an FX-603P is far easier and less likely to ruin a beautiful calculator.

I really wish I'd kept the book of FX-602P programs I wrote. Some real gems in there.


Pauli

I'd second that. The FX-603P is a very nice calculator. They are expensive, though, and aren't quite as nice in the hand as a 502P or a 603P. Just a bit bigger and more plastic on display.

The problem with my 602Ps is that none of them work. they look nice but either the display has gone or the electronics has died. Hence the replacement PCB. The FX-502P, however, seems to survive much better, and few don't work. The FX501P seems to have a display seal problem as both of my examples have black screens.

Andrew