C64-Keyboard-Controlled-Kernal-Switch
This is a Kernal Switch for the Commodore C64, which does not requires any case modifications. The Kernal is selected by holing RESTORE and pushing a number key.
Jusrt holding RESTORE for several seconds will reset the C64. The index of selected Kernal is stored non-volatile, so the last selection will be executed after a power on.
Find some info on the required cable making on my website
Watch the introduction on youtube: https://youtu.be/pfJxfMYcyzs
The Kernal Switch works in conjuctuion with a Kernal Adaptor:
https://github.com/svenpetersen1965/C64-Kernal-Adaptor-Switch-short-board- for ASSY 250469 Mainboards
https://github.com/svenpetersen1965/C64-Kernal-Adapter-Switch-Long-Board for all other Mainboards
I want to thank MindFlareRetro (https://www.youtube.com/channel/UCBbbiZC2YodIp2Pi-lywG-A/featured) for reviewing my documentation.
Known Issue
Solved:
Some games/software require an EXROM-Reset, because they change the reset and/or NMI vector. Then the reset does not jump, where it should jump. It even seems, that the problem is persistent even after a power off. Don't panic... your C64 will function again, later. It seems, those games leave some traces in RAM, which have to get lost after being powered off for a while.
This can be solved by also holding EXROM low while the reset. One of the two reserved IO pins in the pin header can serve to assert EXROM. The software will be changed and the result will be tested.
The problem stated above is some kind of copy protection and is described in detail here: http://tech.guitarsite.de/cbm80.html
Software Rev. 0.1
This software fixes the issue described above. An aditional connection is required. J4, Pin 5 (RS1) has to be connected to the EXROM signal (Expansion port, Pin 9, which can easily be accessed inside the C64) via a 220R resistor. The documentation has been updated.
Software Rev. 0.2
This software makes use of the last free GPIO pin on J4 (Pin 6, "RS2" on Rev. 0 or "RESIO" on Rev. 1). A LED, that is connected there, will be on most of the time. When holding the RESTORE key and the time (about 3 seconds) is elapsed to initiate a "normal" reset, the LED switch off for a short time. Holding RESTORE for 5 seconds will initiate an EXROM reset. The LED signal should help to release the RESTOR key in time for a normal reset.
Board Rev. 1 already provides a current limiting resistor for an LED (R9). A value of 330R is suitable for a red, green or yellow LED, 50R is suitable for a blue LED.
Board Rev. 0 does not provide this resistor. Here, a resistor has to be installed in the LED cable. DO NOT try to connect an LED without a resistor!!! Theis can damage the LED and also the processor of the Kernal Switcher.
REV. 1
Revision 1 is released. The hardware Rev. 1 is tested ok. The documentation is finished.
Calculation of the component prices
The BOM v1.1 was calculated. The total price of the components is 5.98€, which does not incluse any shiping fees. The cables were not calculated.