Re: apple II roms and eproms

[Patrick Schaefer <PSchaefer@epost.de>]

Igor schrieb:

> My eprom burner can't burn eproms greater than 2764 (it's an AP-64) so
> at the moment I can't copy IIgs roms but I'm sure that I'll be able to
> find the images somewhere if I'll ever need. 

Get a 27256 pinout and locate A13 and A14. Connect these pins to a DIP
switch so you can apply +5V or 0V to them. Now you can treat a 27128 as
two 2764 (one with A13 low, one with A14 high). A 27256 is equal to four
2764.

Many 27128 and nearly all 27256 require a programming voltage (Vpp) of
12,5V instead of 21V. To change Vpp, connect a 12V zener diode from Pin
1 of the EPROM socket to ground (the cathode ring points towards Pin 1).

You don't need this modification if vou just want to read out the ROMs.


Patrick