Sometime back I modified my C64c with a switch to change between the original kernel and the JiffyDOS kernel. I did this because JiffyDOS is incredible for loading games from the SD2IEC but it doesn’t support loading from tape at all.
I needed to make another one up. Turns out I forgot how to! so here it is mainly for my own sanity.

• Get a 27C256 eprom
• Get a copy of the original C64c kernel. This should be 16KB in size, if its 8KB then that’s from the older breadbin C64.
• Get a copy of the original C64 basic ROM. This is number 901226-01. This should be 8KB in size.
• Get your copy of JiffyDOS for the C64. This should be 8KB in size.

Place all these files in a directory and open a command prompt (assuming your using Windows).

I renamed my files to something a bit more meaningful, “kernel.bin” “basic.bin” and “jiffy.bin”.
Type the following command:
“copy /b kernel.bin+basic.bin+jiffy.bin new.bin”

This creates a new binary file called “new.bin” and it should be 32KB in size.

• Burn “new.bin” to a blank 27C256 eprom
• Lift up leg 27 of the eprom so it doesn’t make contact with the socket pin.
• Solder the common leg of a switch to pin 27
• Solder one side of the switch to a 4.7k resistor connected to +5v
• Solder the other side of the switch to GND

This should now give you a fully working switchable C64c.

Note: This only works for the newer C64c version. A 27C256 eprom isn’t pin compatible with a breadbin version without more modifications.
Also, JiffyDOS is still being sold and is not downloadable from my site nor will I provide it to anyone asking.