Re: Copying ROMS ?

If this were a situation of shared address lines, with some sort of
decode within, then the 27C64s would not work, unless there was some
change to the board. But I have two identical systems, one with
27C64s and one with the masked ROMs.

I'll disassemble them later and look for board changes.

> Pin 20 is the output enable. The other pins of the ROMs, what are
> their addresses? In particular compare them to a standard 2764 pinout.
> I suspect you will find that some of them are higher order address
> lines being used by the ROM as Chip Select logic.
>
> http://www.arcadecollecting.com/info/eprom_pins/2764.txt
>
> John :-#)#
>
> At 01:11 PM 21/06/2002 -0700, Mike Davis wrote:
>
>
> >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
> > > > > >
> > > > >
> > > > >
> > > > >
> > >
>
Received on Fri Jun 21 13:56:23 2002