4 kernals on the same eprom?

[piemmeweb]

hello, anybody know how to put and use 4 different kernals in the same eprom? I'd like to change the c64 mode kernal in my 128D and maybe on my c64) and like to have 4 different kernals on the same 27256 eprom but don't know how to swap they. what's the pins to shortcut? thanks

[Mark Smith]

Hi there,

Isn't the C128 kernal 16Kbytes in size ?  Which means you'd only get 2 images into a 27256.  And you'll want to use 27c256s as well they use less power.

From memory for  a 27c256 you want to connect A14 to Vcc via a pull up resistor (4.7K ?), and connect A14 to GND via a switch.  when the switch is off you get 1 bank when it is on you get the other.

I've a nice schematic somewhere that has all this, when I get home I'll hunt for it.

I think you might be wanting to use a 27c512 and then use a rotary switch + resistors to choose the kernal you want.

Mark

[piemmeweb]

Well, how to switch 4 kernals on a 27512? and how to switch 4 kernals on a 27256 using it in a C64 (with 8k kernal)? thanks