Re: Copying ROMS ?

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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
> > > > >
> > > >
> > > >
> > > >
> >

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Received on Fri Jun 21 14:26:23 2002