Re: Upgradeable? Can we create
All you need to do is to open the Arc4 up and see what processor is in there. Then, go to the manufacturer of the processor and get a dev kit. Should be a couple hundred or so. But then you will have to develop all software from scratch.
It probably uses a standard programming interface for that unit. Just a wild guess, but the interface is likely RS-232 signals carried over a TTL line. That is common for tiny processors, although some use a JTAG interface.
I would be willing to bet $100 that the "security" bit is set on the processor, so you cannot get the code off of there. The best that you will be able to do is to erase the whole thing and start from scratch. But if you are VERY good at programming, you should be able to cobble something together that will work.
I once saw a board made in the 1970s which, after it was assembled, they placed the ENTIRE BOARD face-down on a belt sander. This completely obliterated all markings on the chip. If Peter and Henry did something like this, then you do not even know which brand of processor they are using. Then, you are out of luck...