Switchable EPROM

[Ross Myers]

>I am a student and for a class project I am researching the best way to
make a >switchable Eprom for a GM P-4 computer,  the normal Eprom is a
27c128, I would >like to have 10 different programs loaded for testing in
back to back conditions.


Wow, 10 different programs!! O.K if you must...
Anyway, I'd use a 27c010, you'll get 8 different programs that way, then
what you need to do is switch address lines A14 - A16 on the 27c010 high or
low depending on which memory area you wish to select. A0 - A13 will remain
connected to the ECM but the address area will be switched by A14 - A16.

So with A14 - A16 all low memory area 00000h - 07FFFh will be on A0 - A13
if you make A14 high and A15 & 16 low you will get 08000h - 0FFFFh and so
on.

You place your different maps in each 32K memory block, and access them via
the binary combinations of A14 - A16.

Make sense?.

Ross Myers