But note that the original EPROM chips did not support electrical erase. And applying UV light meant bulk erase.

So the use of a single external EPROM would not allow the lower part of that EPROM to contain a loader handling any serial port and then have that loader receive more program to burn into upper parts of the EPROM - especially since the EPROM would not run the processor while being programmed.

Even most flash chips have the limitation that they can't serve out code while having other flash sectors being erased/reprogrammed.

So the simplest solution would be to have two memory chips. One EPROM or flash chip with a boot loader. But how (?) would that program get a boot loader when there are no stand-alone programmer available to program it?

The second memory could be a RAM or a flash, and could get the contents by the boot loader program.

But no - there would not be anything simple about the above. So we would be back to my original post.

Yes - a programmer can be written. Yes, the processor can be used. But it would cost. It would take time. And it would probably not work because it would require too many individual steps to be correct. And someone who starts from scratch would not have the equipment and experience to figure out all the broken steps until the design finally started to work.

A fraction of that time and a fraction of the cost, could be used to buy a development board with a modern processor with a RS-232 or USB interface where a PC program could send a new program. And with a modern processor that would have internal, hardware, support for debugging of the downloaded program.

Going the new route, would mean lots of time available to learn new skills on a working platform.
Going the old route would give lots of experiences that may not be wanted at this time. Like 100 different things that can go wrong ending a project in failure.


And what situation would that be? You starting from scratch, without any existing software? No existing hardware but a dumb processor and one or more UV-erasable EPROM chips but without any UV eraser? No tools to fill that EPROM with contents? No tools to drive raw processor pins to use as a building block for a programmer? No tool capable of receiving RS-232 data from a PC to send into latches to then (together with pulsing of address counters) program the EPROM?

Anyone who gets to this forum with the question the OP had, would be in a position where it doesn't matter what "can" be done. The important thing is that with lacking tools and lacking experience, lots of things that can be done just shouldn't be attempted. Becaus the cost would be too high. Because the failure probability would be too high. Just because other - very cheap - alternatives would allow much more learning in way shorter time.

If you have a $300 old car, it isn't meaningful to invest $3000 to try to get it to run a bit better.

If you have the skills and a truly unique wreck, it might be meaningful to invest $30,000 instead. Just because you will be able to create a museum-class vehicle in mint condition.

This is not a thread where an experienced developer is trying to recreate an important historical artifact, but someone who have a "wreck" on his hands and isn't realizing that the cost it would take to make it usable is higher than the cost of buying a new SDK complete with documentation.