Commodore VIC-20 35K Expansion

After getting my Commodore VIC-20 working with SD2IEC  (Was a blown 7406 hex inverter) it’s now time to build a 35k expansion.

Found a great write up on Ruud’s Commodore site.   A schematic is provided which gives the  VIC-20 35k of expansion memory using 62256  (32k x 8 RAM) and a 6264 (8k x 8 RAM)  chips.

(Update: The original schematic had a error in it, which has now been corrected)

Note: There is another error on the schematic. On IC2, pin 20 should be connected to pin 22, not pin 27

Setup the schematic in Eagle and created a PCB. If you are looking to do this you might want to import the Commodore  library for Eagle which contains all the common parts including the edge connector.

Sent the gerber files to PCBWay

Datasheets for the semiconductors:

Completed assembly:

Insert the expansion PCB into the VIC-20. Component side up (I don’t think its physically possibly to insert it the other way).

Make sure the computer is powered off before you do this otherwise you risk damaging the computer and the expansion card

Blue PCB (v1.1)

DIP Switch Settings:

Switch 1 – RAM 1
Switch 2 – RAM 2
Switch 3 – RAM 3
Switch 4 – BLK1
Switch 5 – BLK2
Switch 6 – BLK3
Switch 7 – BLK5
Switch 8 – 6264 WE

  • All off       – Expansion disabled
  • 6 ON        – 4607 free
  • 6,7,8 ON  – 6655 free
  • 5 ON        – 11775 free
  • 4,5 ON     – 19967 free
  • 3,4,5 ON – 28159 free
  • All ON – 35k

Green PCB (v1.2)

DIP Switch Settings:

Switch 8 – RAM 1
Switch 7 – RAM 2
Switch 6 – RAM 3
Switch 5 – BLK1
Switch 4 – BLK2
Switch 3 – BLK3
Switch 2 – BLK5
Switch 1 – 6264 WE

  • All off       – Expansion disabled
  • 3 ON        – 4607 free
  • 1,2,3 ON  – 6655 free
  • 4 ON        – 11775 free
  • 4,5 ON     – 19967 free
  • 4,5,6 ON  – 28159 free
  • All on        – 35k

For a more detailed write up, see the original designers website.

To run a full memory test have a look at this great program from Mike on SleepingElephant.

PCB’s, assembled cartridges and other accessories can be purchased from myretrostore

13 comments

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    • aero on January 4, 2020 at 03:14
    • Reply

    Cool project! I’m about to build something similar myself based on the same schematic, though I can’t seem to find the value for that resistor network (maybe im missing something obvious)

    I’m assuming its 10k, is that what you used?

    1. I used a 10k resistor. though any value for a pull up will work. 4k7, 6k8, 10k etc.

    • JG on February 18, 2020 at 20:29
    • Reply

    I built one of these from a kit sold on eBay and it worked perfectly. I swapped the DIP switch assembly for one that pointed backwards so it could be accessed without unplugging it from the VIC20 expansion port. Easy to assemble even for an electronics newbie. Thanks!

    • LH on January 26, 2021 at 18:34
    • Reply

    Hi I like your project and I wanted to ask if you would provide me the gerber files that you used. I din´t find them anywhere on your website or github. In case you are interested I only want to make one for myself. Thanks already in advance.

    1. No problem. I will mail you the gerbers to the email you provided.

        • LH on February 5, 2021 at 15:00
        • Reply

        Hi i was now able to build the ram expander but it doesnt really work. The problem ist that as soon as I activate the dip switches to control CS and CE for ic2 (the 8kb chip) the computer refuses to boot and when it does boot its very unstable. Also i have verified that the cartridge port works with a 8kb game cartridge. Maybe you can help me. Thanks already in advance.

          • LH on February 6, 2021 at 09:03
          • Reply

          The issue has been resolved. It was a contact issue inside the dip switches.

      • Elmar on January 28, 2021 at 09:44
      • Reply

      Hello LH, Greg:

      Would you mind to share the gerbers also with me?

      Thanks in advance

    • Elmar on January 27, 2021 at 11:52
    • Reply

    Hello Greg:

    Would you be so kind to mail the gerbers to me as well? I would like to build one of these.

    Best Regards, Elmar

    1. I will email you a copy of the gerbers.

    • Jon W on February 2, 2021 at 04:53
    • Reply

    Thank so much for putting together this project and documenting it so well. I would also like the gerber files as well if you don’t mind.

    • Jon on February 3, 2021 at 20:08
    • Reply

    Great work on documenting this project. Could I bother you for a copy of the gerber files as well?

    • TonyG on March 28, 2021 at 00:03
    • Reply

    Just bought the PCB from ebay. Ordering parts from Digikey now.

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