Work has started on a 6.0 version of the C64 core. A release is planned for late 2026 or early 2027. This page gives you an overview on new features as well as download links for untested Alpha versions.

The current Alphas focus on enhanced compatiblity especially with cartridges.

Download location

The current Alpha 15 version can only be downloaded in the Discord Channel:

https://discord.com/channels/719326990221574164/794775503818588200/1508182265870422038

WARNING! DANGER! READ THIS!

A lot of C64 cartridges and other software will be buggy when the REU is turned on. Please make sure to only activate it when you know that the software or cartridge you are using actively supports it. Turn it off again when you do not need it. Anything that does not say “Works better with REU” should be considered incompatible with a REU. Currently the UI not only allows dangeous combinations - unless you turn the REU off it will be on even after rebooting the C64. This behaviour will be made less dangerous in a future version.

Why are we yelling this? Because we ourselves have fallen into this trap during testing and chased non-existent bugs for a while. So this WILL happen to you too.

EVEN MORE DANGEROUS! READ THIS TOO!

The .zip file of the Core now includes an new config file that needs to replace the old config file in the C64 folder of your SD-Card. This is important. Also, you then absolutely can not go back to earlier Cores. This will damage the config file. Yes, we will fix that soon. For Alpha testing, please make sure do not switch between V5 and V6 cores. (If you really need to, keep seperate SD-Cards for the V5 and V6 core). We currently though see nothing that does work with V5 but not V6 (with the exception of the RTC, see below).

List of new features

Changes for physical cartridges

This version has generally improved hardware cartridge compatibility, thanks to two fixes that benefit cartridges beyond the ones we explicitly tested: more faithful timing on the Expansion Port (signals at the cart connector now reproduce real-C64 setup and hold relationships), and proper Ultimax-mode memory mapping (previously the C64 core saw floating data in some memory ranges instead of cartridge-provided RAM/ROM).

Changes to the simulated REU

The simulated REU can now be used in parallel with simulated or physical cartridges. This is very useful for some games, the Snappy ROM (see below) and the Final Cartridge 101%. This feature still needs more testing.

Also some register changes enhanced the compatibility, so the fREUd demo now works flawlessly. There are no known incompatiblities of the simulated REU with a real one.

Physical REU cartridges still can not be used!

SRQ support for the IEC Bus

The IEC bus now has the SRQ signal wired into the Core. This is usually not needed at all on the C64 (only the C128 really supported the SRQ signal) but the Meatloaf cartridge actually requires it for it’s PTERM app. So now this aspect of Meatload works!

Simulated Freezer Carts now use F9

Starting with this Alpha release, the Freeze function has been moved away from the Restore key to the F9 key. The Restore key now only issues an NMI like on a C64. This enhances compatibility with all known Simulated Freezers.

Final Cartridge 3 Support

The current Alpha release adds full functionality to the emulated .crt cartridges for the Final Cartridge 3.

We recommend visiting https://www.freepascal.org/~daniel/fc3/ to download the V2 .crt image and check out the documentation you can find there. This cartridge adds a lot of the features that you would expect when you have used the Freezer-feature on the MEGA65. Press F9 to access the features.

Please test the combo of the simulated REU together with this specific enhanced Final Cartridge Software. It allows something not possible before: Enter the monitor, make changes and jump back into the running program. This requires the extra REU memory.

Without the simulated REU the cartridge freezer now works fully, allowing you to make “snapshots” of games that have no save function. Please note that freezing requires an empty mounted disk. More detailed instructions will be published soon.

SnappyROM and Super Snapshot

The current Alpha release adds the Super Snapshot and the SnappyROM to the list of emulated .crt cartridges. SnappyROM together with the emulated REU makes an excellent development system, check it out. To simulate the freeze button, tap the F9 key.

Action Replay support

The Action Replay .crt type should be working now. To simulate the freeze button, tap the F9 key.

MagicDesk 2 support

The current Alpha release adds support for the “MagicDesk 2” .crt format. This format is used for the SNK vs. Capcom project.

Wonderboy (OCEAN) support

Support for another .crt type - Wonderboy (Ocean) works now.

IDE64 Support

The IDE64 cartridge is supported by the current Alpha version of the Core. There is no IDE64-simulation, you need an actual interface cartridge. This is still experimental - we need data whether this fully works from users. Early feedback is great though.

IDUN Support

The Idun cartridge, a project that marries a Linux-Raspberry Pi with the C64, is now compatible with the latest Alpha of the Core.

RTC disable

The current release of the 5.2 core emulates a Real Time Clock connected to the C64 tape port, mainly to run with GEOS. Unfortunately a very limited number of programs will crash when this clock is active. The current 6.0 Alpha turns the clock off again, so these programs will run, but you will lose the RTC functionality. Later versions will make the clock switchable in the User Interface.

More details about the RTC can be found here.

Proper C64 RAM initialization

The current Alpha core fixes the RAM state of the C64 at power on. It now has the famous “00 00 FF FF FF FF 00 00 00 00” pattern. This fixes some programs that rely on certain memory locations initializing to a 00 or FF (sometimes as copy protection), for example Q-Bert.

Other features planned

To see a list of features that are planned, please check out the list of issues labeled “V6” in the Github of the C64 Core. You can directly access this list here. This is not a guarantee that these features will be implemented, everything is under evaluation.