Reasons for scarcity of working TI-58C machines

[Garth Wilson]

(06-17-2023 08:54 AM)blackjetrock Wrote:  You could probably replace the RAM interface chip and RAM chip with a modern microcontroller like the RP2040. Non volatile storage can then be done by using the flash of the microcontroller. No battery required. You do need some 'scheme' to interact with the microcontroller and tell it what flash to load and save to.

Good idea, to use a microcontroller, to keep lots of these calcs alive where otherwise there'd be no hope.  I seem to have one of them.  I'm sure the nonvolatileness was from the battery continuing to provide power though, with CMOS memories' current being negligible when they're not selected and the power-supply voltage is in the retention range, below the operating range.  In 1986 at work I observed an 8KB SRAM holding its memory overnight on only a 10uF capacitor.  I did not try to see how much longer it could go.  Flash memories have a limited number of writes before they're worn out though.  The number has gotten super high for file storage, but not for use as RAM.  They also take much longer to write than they do to read (although that might not be a problem for a calculator as slow as the 58c), and you might have to write a whole sector just to write a byte, and even if it has a byte-write instruction, it might put the whole sector in a buffer, change just that one byte, and write the whole sector back, adding that wear to the whole sector.  I've worked with flashes that do that.  Non-flash EEPROMs don't.