• Fix any RAM or main ROM issue on your Commodore equipment
• Expand your RAM up to 32 KB

Project tested and working

Supported equipment: PET / VIC-20 / 2031 / 1540 - 1541 / 1570 -1571 - 1571CR FDD

This board can be use for upgrade, fix or diagnostic an issue on Commodore PET / CBM (including PET 2001/N, 3032, 4032, 8032/8032SK, etc.), Commodore VIC-20 and Commodore 1541 disk drives. It's a not invasive replacement, unless the 6502 is soldered on the board: in this case you need to un-solder it and put a socket in its place.

This board allows to replace the RAM and/or the ROM (except for the Characters ROM). You can use it to diagnostic any problem about the RAM or ROM (BASIC, EDIT, KERNAL) of your computer or drive, to fix a problem or also to upgrade the firmware or install up to 32Kb of RAM. The board can be also left inserted into the computer or the drive for constant use.

Note: if you want to permanently install it in the Commodore VIC-20, you will probably need to solder the board directly on the VIC-20 board, because of the tight space behind the keyboard.

Building tutorial:

Bill Of Material (BOM). You can also download it as .xlsx file from this page

1) Solder IC5, IC6, C1, C2, C3 and the resistor pack (see azure boxes).

LEAVE JP1 EMPTY!

VERY IMPORTANT: DO NOT USE A SOCKET FOR IC5 AND IC6!

2) Put 2x 20 turned (lathed rounded) pins headers from the bottom side. These headers will be inserted in the 6502 socket on the computer board. Don't use headers with thick pins or it can damage the 6502 socket. To keep the headers aligned, I suggest to insert them into a DIP socket before to solder it.

The yellow boxes show where the headers should be soldered on the top side.

3) solder the sockets and the DIP switch pack (red boxes) and you're almost done!

NOTE: THE "ON" side of the DIP switch must to be put close to the resistor pack

4) You only need to solder a wire from the CPU to the GAL chip, based on this scheme.

DON'T SOLDER BOTH WIRE! JUST ONE IS NEEDED!!!

Since PCBWay will send you a minimum of 5 boards, if you need to use it for PET, VIC-20 *and* 1541, I suggest you to build 2 different boards instead of using just one board and keep changing the wires.

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5) Now you need to program the FlashROM chip with the ROM image of your computer. Since the original ROMset is split in more than a chip, you need to get the ROM images from the web http://www.zimmers.net/anonftp/pub/cbm/firmware/index.html is a good place), pack them together in the right sequence and upload to the FlashROM.

However, to make your life easier, I put here the file ROM and GAL binaries.zip that contains ready to use images for the most common computers. I assume you know how to program a FlashROM; if not, you will find plenty of examples on Google.

The same zip file also contains the images for the GAL chip. You need to program it using the right JDE file, accordingly with your needs.

If you don't own an EPROM programmer yet, I suggest you to buy a MiniPro / TL866 II programmer. It's quite cheap, especially if you go to Aliexpress or eBay and get a clone (as I did).

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6) After you programmed the two ICs (flashROM and GAL), it's time to populate the board with all the missing ICs. Put the RAM, the FlashROM and the GAL. If you haven't a spare 6502, you can remove the one of your computer or drive and use it.

7) Time to put the board into your computer or drive. Take care to install it using the original orientation of the 6502 (the notch in the chip must to be put in the same way). BEFORE TO SWITCH IT ON, however, you need to set the DIP Switch accordingly with your needs (see tables below).

REMEMBER TO ALWAYS SWITCH OFF THE EQUIPMENT BEFORE TO CHANGE THE DIP SWITCH or you can burn or damage something!

If you're trying to diagnostic an issue, activating or deactivating the RAM and / or the ROM can pinpoint you directly on the problem. And, of course, you use the equipment leaving the board installed.

Enjoy your Commodore equipment!

Switch table:

Note: this is a revisited edition of a +20 years old freeware project apparently no more supported by his developer (I wrote him many e-mails during the last years without any answer), so I updated the board, wrote the documentation, packed the firmware and put here for everybody. Hope you will enjoy!