[souprock]

The proper fix is to store user data and run user code only when removable media is inserted. The calculator could hardware-disable flash writes when removable media is detected, and then do a full reset when removable media is removed.

Ideally it would be an SD-card plugged in at the top edge of the calculator. The area around that connector could be clear plastic, with visible circuit traces running to the CPU.

[lozaning]

If they came out with something like this I bet someone would just start selling modchips.

[souprock]

It'd be less likely than with the currently selling calculators. Are we seeing modchips now? I don't think so.

Of course it is always possible to fully replicate the calculator. I'm sure there is a Chinese factory that could do it. Stopping a trademark violation like that is the job of the port inspection and customs enforcement people. The situation becomes like illegal drugs, but with much lower demand and much more difficult production.

Simply replacing the chip is some serious electronics work. These aren't socketed DIP chips. They aren't even BGA. TI puts the bare naked silicon chip right on the board, bonds wires from it to the board, and then covers it with a blob of black glue.

My suggestion of clear plastic makes this even harder. Modifications would need to look normal. The part of the board between the SD card socket and the CPU should have a minimum of clutter and a colorful boarder box, making it easy to see where one should look for modifications.