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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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?
Author
I used a 10k resistor. though any value for a pull up will work. 4k7, 6k8, 10k etc.
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!
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.
Author
No problem. I will mail you the gerbers to the email you provided.
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.
The issue has been resolved. It was a contact issue inside the dip switches.
Hello LH, Greg:
Would you mind to share the gerbers also with me?
Thanks in advance
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
Author
I will email you a copy of the gerbers.
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.
Great work on documenting this project. Could I bother you for a copy of the gerber files as well?
Just bought the PCB from ebay. Ordering parts from Digikey now.