I have buzzed out the ROMs in the circuit and all have common pins except pin 20, which is different for each one. That seems as I would expect for normal chip selects. Something is really odd here! Mike
I've not heard of copy protected ROMs, shouldn't be possible -as how would the CPU then read them? At least in those days...
AS for the non-reading, perhaps there are unusual chip selects, it was common then to wire the board with shared address lines, and the chip selects built into the ROMs would choose which one was active when a certain address combination was reached. This would be the high order address lines that are not used by 2764's directly, for example you might find that address 13 - 14 are tied to pins 22 and 24, with internal logic on the ROMs that would allow three ROMs to be shared (you want them off for one combination of A13-14).
John :-#)#
At 11:42 AM 21/06/2002 -0700, Mike Davis wrote:
Someone else pointed that out. I have replied to the list with the ROM part numbers.
But I have two identical machines. In one, I have these ROMs, in the other, I have 27C64s. Wouldn't that suggest that they are identical pinouts?
Mike
I seriously doubt vintage ROMS are copy protected!
What is the ROM (EPROM) type you are using and what are they marked as?
You might have a custom masked rom with inverted chip select or such.
Kev
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