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Zzyzx

Strange name, so what is it?

Well, the idea came about when my workhorse C64C started playing up and I had to switch to my nice breadbox C64 which I don't really like to use because it is in very nice condition. Anyway, I came to hate the fact that it had no reset button, nor did it have a fast load kernel ROM in it, but, I didn't want to cut any holes in the case to fit a ROM switcher or a reset button. So I came up with a design that can do all that without any external switches or buttons.

So what does the Zzyzx do

Simply put, it just monitors the C64 keyboard and generates a reset from that or switches the kernel ROM (if you have a multi Kernel set-up).

To reset the C64, you hold the restore key down for about 2 seconds and the C64 will reset, Zzyzx has a dedicated output for the reset function. This works exactly the same as any other reset hardware out there and is always active.

To switch kernel ROM's on a multi-kernel ROM arrangement you just press F1, F3, F5 or F7 within the first 2 seconds of the C64 being switched on and it will select the desired kernel and then reset the C64 for you. Or hold down Left-Shift (or Shift Lock) and press F1, F3, F5 or F7 for the same kernal selection but another spare output is also switched. After the initial power up timer has expired the F1-F7 return to normal function and will not change the Kernal selection.

There is three outputs on the board that can be used for anything really, but the most common application would be to switch the address lines on a multi-kernel arrangement using the first two outputs, the third can be used for anything you like.

Here's how it's operation looks as a table:

F1 Key = 000, MultiROM Bank 1, with Aux out off F3 Key = 001, MultiROM Bank 2, with Aux out off

F5 Key = 010, MultiROM Bank 3, with Aux out off F7 Key = 011, MultiROM Bank 4, with Aux out off

F1 Key + L-Shift = 100, MultiROM Bank 1, with Aux out on F3 Key + L-Shift = 101, MultiROM Bank 2, with Aux out on

F5 Key + L-Shift = 110, MultiROM Bank 3, with Aux out on F7 Key + L-Shift = 111, MultiROM Bank 4, with Aux out on

The selected kernel is stored in the AVR's EEPROM so you only need to select once (unless you want to change Kernels). Then on each power up (or reset) the selected Kernel ROM will automatically be selected. Note, the Kernel ROM is not stored in the AVR, just the states of the ROM bank select pins.

Fitting the unit is pretty simple, just pull the C64 apart, remove the keyboard connector, fit Zzyzx over the top and plug the keyboard back in to Zzyzx. You will then need to connect your Multi-kernel ROM to Zzyzx. On some models you will also need to do a little bending (or cutting) of the tin foil shields inside the C64.

The cost per ROM switcher is $35 AUD (Australian dollars), this price includes worldwide postage in a padded bag. If you require more than one the postage cost may rise by a few dollars, contact me for an exact quote.

They are only available as a fully assembled unit.

Number in stock ready to ship: Discontinued!


  • keyboard_switch.zip Keyboard Switch development files

  • Important:

    There is some soldering required to fit the wires to the C64, if you aren't confident enough to disassemble your C64 and fit this product then maybe it's not for you.


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