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This is a drop in Kernal ROM replacement for the Commodore 64 Longboard variants (ASSY 326298*, KU-14194HB, 250407, 250425 and 250466). It can hold 4 Kernals that are selectable using the RESTORE key on the C64. These come ready made and preprogrammed with a licensed copy of JiffyDOS along with JaffyDOS, EXOS and the original Commodore Kernal.

ASSY 326298 requires a fix to the reset signal. You can find details on how to do it and a few other fixes for this board here

This is based on the C64 Kernal Switcher by tebl. Which in turn is based on the SKS64 switchless Kernal switcher by bwack.

Designed by BWACK. CERN OPEN HARDWARE LICENSE v1.2 http://www.ohwr.org/

The CAD files are available on GitHub: https://github.com/bwack/C64-Switchless-Multi-Kernal-27C256-adapter

All text above must be included in any redistribution**

The version here was made in an effort to shrink everything down to the physical size of the original 2364 mask ROM and place everything on the underside, similar to my other replacement ROMs available on Tindie. This results in a very neat looking package leaving only the silkscreen text on the topside.

Install

Remove the Kernal ROM at U4 on the C64 and insert this replacement. If your Kernal ROM is already socketed, no soldering will be required. Connect the two included hook clips from the RSET pin on the Kernal replacement to the RESET line on the C64 mainboard. Likewise connect RSTR to the RESOTRE line. You can cut the hooks off and solder the wires directly if you prefer. Please see images for the easiest location to find these signals for your board revision.

Finally connect the orignal power LED to the pins labelled LED+ LED- LED+, the orientation does not matter they are the same when flipped. Note some C64s have a shorter LED cable that may not reach over to the Kernal ROM, in this case you can use the included male to female dupont wires to extend the power LED cable.

Usage

When you first power on the system you should notice the power LED flash rapidly for a second, if this does not happen double check your RESET and RESTORE wires are connected to the correct places on the C64 and that you have plugged the power LED into the Kernal ROM and not the original C64 LED connector.

On first boot you should be greeted with the original Kernal and everthing should look as normal. Holding the RESTORE key should cause the power LED to flash once every second or so, this is how we control the switcher and releasing the RESTORE key will "confirm" our selection.

• 1 flash: Resets the machine
• 2 flashes: Move to next Kernal
• 3 flashes: Jump to 1st Kernal (910227-03)
• 4 flashes: Jump to 2nd Kernal (JiffyDOS)
• 5 flashes: Jump to 3rd Kernal (JaffyDOS)
• 6 flashes: Jump to 4th Kernal (EXOS)

Why these Kernals?

I chose these because they suit most common situations which I'll cover below. There are many other Kernals out there but a lot of them are more specific in their use cases.

901227-03: The final version of the original Commodore 64 Kernal. This is a must have for full compatibilty and cassette support, and it feels like home. This is my go to when using a datasette or in the super rare case I find something that doesn't work with the other Kernals.

JiffyDOS: Undoubtedly the most popular Kernal replacement. It offers around a 10X speed boost when paired with JiffyDOS in the 1541 or SD2IEC (which supports Jiffy routines) and pi1541 (requires the 1541 JiffyDOS binary). There is also a huge amount of shortcut keys, some of which provide added functionality over the original C64 Kernal. The trade off is some slight compatibilty issues with certain software and the removal of cassette support, although you'd be hard pressed to find something these days that doesn't work with JiffyDOS. This is my go to when paired with a 1541 with JiffyDOS.

JaffyDOS: As the name suggests, it's very similar to JiffyDOS. The biggest difference is the built in file browser. It was originally designed by Jani to work with the SD2IEC but also works the 1541 and pi1541, although full functionality is not guaranteed. Cassette and RS232 support is removed to make way for the extra features. As Jiffy is required to build Jaffy it made sense to just include both. This is my go to when using the SD2IEC and pi1541.

The function keys for this version of JaffyDOS are as follows:

• F1: @"$" Display directory CR
• F2: @ "CD: Change directory CR
• F3: / LOAD"",8,1 CR*
• F4: @ "XS: Mount swaplist CR
• F5: ↑ Load and run a basic program CR
• F6: @ "CD:← Up one directory CR
• F7: @FB: Launch filebrowser CR
• F8: @ "S: Scratch file

CR Indicates the command will be executed automatically after pressing the F-Key.

EXOS: Originally published in the German 64'er magazine by J Schemmel, EXOS is a fastloader that doesn't require any modifications to the disk drive. It offers a speed boost similar to that of JiffyDOS but without the solid compatibilty JiffyDOS offers. While a lot of programs will play nice, expect issues with software that includes its own fastloader routines, or things that rely heavily on the original 1541 timings (many modern demos). It will also have issues if JiffyDOS is enabled in the 1541 drive, and requires a different version for PAL and NTSC (hence why there are two options to choose from). Just like Jiffy and Jaffy it does not offer cassette support. This is my go to when using a stock drive that doesn't have JiffyDOS.

I also made a slight modification to the EXOS kernal to better match the colour scheme and layout of the other Kernals.

I have chosen to handle purchasing of the JiffyDOS license for each ROM so you do not need to worry about it. I will not be providing ROMs that include JiffyDOS or JaffyDOS without a license, regardless of whether you already have a licensed version so please do not ask.

All boards are hand assembled and tested before shipping. As these are hand soldered, flux residue is included with every board at no additional charge ;-)