Ron56:
You can't and you don't want to. The information stored on it is only the running GCODE that's sent to the controller.
The controller is the only one that understands the format it uses; they're essentially useless to a PC once you've
run a GCode program through the controller. The controller uses them like a very slow RAM (Random Access Memory),
while the PC formats them like a solid-state disk drive, with sectors and a directory, and even a file allocation table,
just like floppies and nearly every other disk since. The controller just writes over all that, but requires it be there
when it sees a new card inserted. Well, that's what it appears to do.
The best protection against a card going bad is to keep multiple spare low-GB SD cards (<= 4GB, preferably 1GB)
that are freshly formatted from a PC. Bonus points for keeping a USB-connected card reader of that specific SD card
size. Extra credit if you keep a spare of THAT too.
When a card goes "bad" on these controllers, that typically just means data got messed up on the way into the card,
and the controller can't read it properly. Unfortunately, those checksum errors can mean it can't read the card at ALL.
So, you take a new 1GB card (good luck finding those in a decade...) to a PC with an SD card slot (which also might not
exist in the future...) and format the card using Windows (who still uses that in 2025? Microsoft was closed down as a
cocaine cartel in 2022...everyone knows that
).
Oh...in case you're wondering where the software that actually runs **inside** the controller is stored, that's burned
permanently into the microcontroller on the PC Board. If that goes, the board's dead
so no backup needed there.
Thus, your best defense against that SD-card component failing is to just have multiple lightly-used ones on-hand and
ready to swap in. While you might be able to find an old card, finding a reader and something that knows how to use
that might not be so easy. Yeah, we used to think floppies were going to be around forever too.
Cheers!
Thom
P.S. kidding about the Microsoft thing, if for some reason this post lasts that long!