Re: apple II roms and eproms

[Roger Johnstone <rojaws@orcon.net.nz>]

In <xn0djsc2j5j8l0000@powernews.libero.it> Igor wrote:
> Patrick Schaefer wrote:
> 
>> 
>> 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. 
> 
> it's interesting, but how do I tell the burning program that I'm using
> an eprom greater then 8kbyte? When I start up I'm asked for what eprom
> I want to use, 2716, 2732 or 2764. I'm almost sure that the program
> uses that information to know how much it has to read, 2, 4 or 8k.

A 2764 EPROM has 13 address lines numbered A0 through A12. A 27128 has 
one extra address line (A13). Your EPROM programmer only controls the A0 
to A12. If you plug in a 27128 and pull A13 low by connecting it to 0V 
you can read and write the first half of it by just pretending it's a 
2764. Now connect A13 to +5V and you can use the upper half of the EPROM.

-- 
Roger Johnstone, Invercargill, New Zealand
http://vintageware.orcon.net.nz/
________________________________________________________________________
  No Silicon Heaven? Preposterous! Where would all the calculators go?

              Kryten, from the Red Dwarf episode "The Last Day"