k3ys

Hi David, The issue with the black screen is probably the same VIC-20 quirk as with a regular 1541. The 1541 puts residual power on the IEC reset line which back feeds into the cartridge port through a pull-up resistor. Its not much current but it is enough to cause modern low power RAM chips to hold their contents even when the VICs Power is off. Holding the cart reset button for a second or two while the VIC is turned off shunts that current to ground and clears the cart memory. Im not sure it this is the case for the Pi1541 but theres a good chance thats the whats causing the black screen.

Well, don't hold your breath on that one. It'd take quite a bit of design and testing. But that's how I'd do it.

I'm not sure I could handle wasting that much RAM! Heheh. If I did do a board with a 64K chip on it, I'd do something that would let you bank all of it wherever you like, even switch banks in and out using an I/O register.

@carlsson, I have a new version of the board made with an AND chip. It uses DIP switch #7 to enable the low 3K of RAM at $0400-0fff. Here's the new eBay listing if you're interested. $25, ships internationally.

Adam's trick with the middle priority decoder bits is clever and let's you decode the BLK signals with one chip. That bottom 3K has three different signal lines so you'd need to OR those together, but since the are active low and the output is active low a 7421 4-input AND would work. And yeah, you're talking about trading spaces with $A000.

Hello all, I'm new here. I like to work with hardware and I've been working on tricking out my VIC-20. I've built a tiny little 32KB RAM expansion that fits inside the cartridge port. It's based on Adam Bergström's circuit from '95 ftp://www.zimmers.net/pub/cbm/documents/projects/memory/vic20/32kB.html. But, I've added DIP switches to it to select how much RAM is enabled. There's a whole cart Enable switch and a Read-only switch for helping to run copy-protected cartridge images. I had a few PCBs made and kept one for myself (of course). I have 7 left for sale on eBay: http://www.ebay.com/itm/331602184425if you're interested. I'll be happy to try and answer any questions you might have about it. Cheers!