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 SLG46620 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.
- The UI for setting the different memory configurations.
- Handling the RESET button for the VIC 20.
- Dimming up and down the button LED when in configuration mode.
Quite ok for a 0.40 USD chip in a TSSOP20 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 2 more gates. One 3 input AND single gate and one 2 input single gate. These combine RAM1, RAM2 and RAM3 as well as IO2 and IO3 into fewer signals.
There is also a TVS for the reset button and 4 LEDS, and some 1µF decoupling capacitors.