I think I understand what you are saying. I'm sure they are Masked ROMS or at least that would make sense. They are a 4 chip chipset with numbers: EPSON BASIC1R0 M64020AA to M65023AA. The thing is however, that in identical machines, the other EPROMS are 27C64 so the pinout would seem to have to be the same or the EPROMS would not work right in the other identical machines, would they? Mike
If they are masked ROMs (like Bally used in their pinball machines) they may have their chip enable lines defined differently from an EPROM.
It is unlikely they have any protection.
Mike Davis wrote:
I have several vintage computers (Epson HX-20). A couple of these have been customized and have had the BASIC ROMS removed and some other ROMS installed.
I'd like to go back to the original BASIC machines. I do have one original HX-20 that has the BASIC ROMs. But when I tried to copy the ROMS into my Data I/O Model 22, only FF shows up. I presume these ROMs are protected somehow.
However, they function and must function in use, so the data should be recoverable.
Anyone have any suggestions on how to make copies of these old BASIC ROMs?
Thanks, Mike