CornBit™ V2 (Programmable ROM)

(1 customer review)

$22.00 USD

ROM failure is a common problem in Commodore 64 and related machines. Named in tribute to the KERNAL it’s meant to replace, CornBit™ is a 100% compatible ROM replacement for 2364 (8KB) ROM chips (i.e. BASIC and KERNAL ROM in the C64 breadbin or VIC 20). Compatibility with 2332/2532/2732 (4KB) and 2316/2716 (2KB) ROM chips is possible, depending on how your Chip Select pins are configured (chip is selected on pin 20 by default, and jumper can be soldered to enable additional chip select on pin 18 or 21). In editions of the Commodore PET that use the 2316, for example, the CornBit™ can be used while leaving the adjacent socket empty. The CornBit™ works great as a character ROM replacement in the C64 as well. Version 2 adds solderable jumper to enable chip select on pin 18 or 21, expanding compatibility.

What’s more, the CornBit™ has 4 different “slots” activated by DIP switches. Use them to have an all-in-one BASIC/KERNAL/Character ROM replacement, multiple character sets, different KERNALs, etc.


The CornBit™ is not intended as a facility to transmit copyrighted content. Please do not purchase CornBit™ if you intend to use it in a way incompatible with copyright law. Please inquire if you need a specific configuration. I will not program them with content that violates copyright.

If you have the BackBit Chip Tester, the CornBit™ is fully reprogrammable with four 8KB ROMs of your choice. This is made possible by the extra pins that hang over on either side. The extra pins only take up a few millimeters of space, so they should not get in the way of other components, but you will have to install CornBit into a socket (dual wipe or machined pins).

Default Configuration:
Slot #1: C64 KERNAL ROM
Slot #2: C64 KERNAL (BackBit Enhanced)
Slot #3: C64 BASIC ROM
Slot #4: C64 Character ROM

To reprogram with the Chip Tester, append four 8KB binary files into a 32KB file. Then those 4 ROMs will be selectable with the 1st and 2nd DIP switches. Make sure to do a binary append. If you have a 4KB ROM, append it twice. If you have a 2KB ROM, append it 4 times. The 3rd DIP switch must be off during programming, and on during usage.

Additional information

Weight 2 oz
Dimensions 1 × 1 × 1 in

1 review for CornBit™ V2 (Programmable ROM)

  1. eightbit (verified owner)

    First review? I feel special 🙂

    I had purchased three of these in order to replace the original (and dying) MOS KERNAL/CHARACTER/BASIC roms. I had already had an original BASIC rom fail on me and I wasn’t about to sit around waiting for the others to fail. Replacements are not cheap anymore either.

    I know these have much more functionality (programmable) than what I am using them for, but I can tell you that these are excellent modern future proof replacements right out of the box for all three MOS chips in the C64. Flip a few switches to tell each one what chip they should act as and pop them in and you are done.

    I have been using them in my C64 for quite a while now and they work as expected, just like the originals.

    At under $20 a piece they are well worth it. And, well worth the peace of mind that these three chips will most likely never need to be replaced again in my lifetime!

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