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Gcart DCNT (Dirt Cheap No Thrills) is the cheapest memory expansion with at least some form of feature-set.
It has only two active parts. A GreenPAK SLG46533V programmable logic device and a SRAM.
The GreenPAK from Renesas a very small OTP programmable logic device with some analog features as well.
It handles;
- The actual memory decoding from BLK1, BLK2, BLK3, BLK5, The lower 3k as well as IO2 and IO3.
- Write protection for BLK5.
- Handling the RESET button for the VIC 20. This gives two additional modes of operandi. Read more here.
Quite ok for a 0.40 USD chip in a 2.5mm x 2mm package.
The other chip is a SRAM with 128k. More than I actually need and use, but it is the cheapest available.
In all honesty there is one more gate. One 3 input AND single gate for combining RAM1, RAM2 and RAM3 into one signal.
The BoM is less than 5 bucks.
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The BoM including PCB, but excluding a custom injection molded case, is less than 5 USD. However, that does unfortunately not mean I will be able to sell it for that. There are a few other cost-items that needs to be covered.
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The design files wil be released as OpenSource once this is fully evaluated. Due to the one time programmable chip you might still want to buy it as a kit at least. To have the chip programmed from factory requires a MOQ of 5000 units, which I thiunk is a bit of a stretch.