Re: apple II roms and eproms

[Wayne Stewart <waynes@telus.dotnet>]

Igor wrote:
> Reading past messages I've understood that AppleII+ roms are not pin
> compatible with eprom chips. Is that true also for Apple IIe/IIc/IIgs
> roms?
> If not, what kind of eproms should I use to back up or substitute them?

The IIe and IIc can use regular EPROMs. 2732,2764 or 27128
I don't recall on the ROM 1 but the ROM 3 IIgs can use regular EPROMs.
If you really need the size I can dig out a ROM 3 that came with
EPROMs and check the size


The II+ ROMs aren't pin caompatible but you can easily make an
adapter to use 2716 EPROMs. From Understanding The Apple II

1. se two 24 pin DIP sockets/If pin 1 is not clearly marked on
the sockets, choose pin 1 and mark it with fingernail polish or
other permanent marking.
2. All pictured wiring is shown in phantom. Pins are bent inward
and wiring is routed on inside of sockets. Use 30 gauge insulated
wire and keep wire lengths as short as possible.
3. Remove pin 21 from lower socket. Save this pin as a spare.
4. Bend pins 18 and 21 of the upper socket inward so they will not
make contact with the lower socket when the sockets are mated. This
must be done carefully so the EPROM will still make contact with the
bent pins when it is inserted into the upper socket.
5. Solder a short jumper between bent pin 18 and the base of pin 20 in
the upper socket. Carefully dress the jumper at the base of pin 20 so
it will not interfere with the mating of the two sockets.
6. Solder a short jumper between bent pin 21 on the upper socket and
the base of pin 18 on the lower socket. Carefully dress the jumper on
the base of pin 18 so it will not interfere with plugging the completed
adapter into the ROM socket.
7. Push the upper socket into the lower socket. Inspect visually or with
an ohmmeter to make certain there is no contact between pins 18 on the
upper and lower socket. With some sockets it may be necessary to modify
or insulate pin 18 on the lower socket so that it does not touch pin 18
on the upper socket. This must be done carefully so pin 18 is still
firmly mounted in the lower  socket.

Api of the adapter
http://www3.telus.net/waynes/adapter.jpg

Wayne