Reasons for scarcity of working TI-58C machines

[blackjetrock]

(07-09-2023 05:36 PM)brouhaha Wrote:  

(07-09-2023 04:41 AM)blackjetrock Wrote:  I've just had a search on the internet and there is a service manual for the TI58 and details about the multi-register IC that provides the RAM storage, so it looks like it would be feasible to replace the RAM with an RP2040. It seems to run off 9V but that's not a problem with some voltage dividers and a driver IC to do the outputs.

It seems to be an unusual device so dropping a RAM chip in doesn't look to be simple.
Best not to throw a broken 58C away. I'll have to try to get a broken one so I can have a go.
Andrew

If the TMC0591 isn't damaged and you just want to replace the RAM, a normal 5V CMOS low power SRAM should work, e.g.6264L. They don't run the SRAM on 10V; the whole point of the TMC0591 was to interface to normal CMOS RAM.

Because the calculator chips are PMOS, everything is referenced below ground. The calculator ground goes to the SRAM Vdd, and the TMC0591 Vdd2 goes to the RAM Vss.

Tie the extra SRAM address lines to Vdd2. Tie the extra SRAM data lines through individual series 22Kohm resistors to Vdd2.

I haven't actually done this, as I don't have a TI-58C.

I don't have a 58C either. i might look out for one though, preferably broken.
I've done lot of RAM replacement with the RP2040 recently, it must be 5 or 6 by now. One was a CMOS RAM that ran with a similar supply regime. That actually ran off 6.4V and that, I think, killed it eventually. I'll have a more detailed look at the circuit.
One advantage of the RP2040 is that you can store RAM images in the onboard flash, giving you NV RAM and also a catalogue of images.


Andrew