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Rick Ethridge
October 28th, 2005, 02:34 PM
I was just given a very well preserved functional VIC 20. What is the easiest method to increase the memory? I have a game cart with a 4K ROM. All the pins are there. Any help appreciated.

billdeg
October 28th, 2005, 03:52 PM
you really don't have to increase the RAM because many games were made for the stock VIC...but you'll see on Ebay on any given day RAM carts that you can buy to boost the system up to 16K.

I have never added RAM to the motherboard, but I am sure that there are all kinds of hackers who have. I would suggest against it unless you're willing to sacrifice a few motherboards in the course of experiementation.

The only problem with the RAM expansion carts is that you then have to load programs via disk drive (1541). There really weren't many programs written for the stock VIC that came on disk. By the time disk drives were popular the C64 replaced the VIC 20.

Here's a link to a picture of a bunch of VIC stuff that I took a picture of from my collection...http://vintagecomputer.net/commodore/vic-20/

carlsson
October 30th, 2005, 12:20 PM
Yes, you use memory expansion cartridges. Of course these work just as well with a disk as a tape. The memory map is divided into eight blocks of 8K. Block 0, 1, 2, 3 and 5 are the ones you can add RAM to. Your game cartridge is probably wired to block 5, so if you replace the 4K ROM with 8K RAM, it will only be useful to load other ROM images from tape or disk. It would be possible to rewire it to e.g. block 1 however, to make a traditional 8K memory expansion.

The largest, but still somewhat common memory expansions are switchable 3+24+8K, giving a theoretical total of 35K memory expansion. No software requires this configuration though.

If you are handy and wish to piggy-back RAM chips to the motherboard, I suggest you try to build (or order) this 6502 ROM/RAM expansion board instead. It will allow an internal, configurable expansion from 3 to 32K, hold four alternative ROM revisions (not so useful maybe) and four cartridge images.

http://people.freenet.de/x1541/hardware/petram.html

vic user
October 31st, 2005, 04:34 AM
This forum has tons of stuff on memeory expansion and the vic 20:

http://sleepingelephant.com/denial/index.html

chris

animekenji
November 10th, 2005, 09:53 AM
I have always wondered about internal memory upgrades for the VIC 20. Either swapping out the existing chips for higher capacity ones or piggybacking more chips on top of them. I have a distant cousin who had a VIC 20 with the Super Expander cartridge and it seemed precarious to me to have that cartridge hanging out the back. I was always afraid a little nudge can unseat it and maybe short out the expansion or the computer. Hmmmm....I wonder if the memory chips in a C16 are pin and voltage compatible??

vic user
November 10th, 2005, 10:08 AM
some people on the Denial forum have done some pretty next things with vic 20's and memory.

one main problem, if you want to call it a problem, with trying to keep giving more memory to the vic 20, is that the way the memory is laid out in the vic does not make it a good candidate for say having a vic 20 with 128k RAM.

there will be others who will probably correct me, as they know more than me, but from what i know, you can only expand the vic 20 to about 37K, and not all of that can be used for straight up programming.

i have one of my vic's at home that is "maxed out" in RAM, and i can only use about 28K for coding, with an additional 5K that i can access through peeks and pokes.

here is a memory mpa of the vic:

http://www.tkk.fi/Misc/cbm/docs/vic20-memorymap.html

chris

carlsson
November 11th, 2005, 03:21 PM
Chris is correct. The memory map allows a total of 31K continuous memory, of which at least 0.5K somewhere preferrably is screen memory. There is another 8K RAM/ROM slot, and a few I/O blocks that are unconnected. In theory you could fill the latter with RAM or ROM, but it would make a very non-standard VIC-20.

Cartridges seldom go loose once they are inserted, much because they are wider than they are tall. Memory expansions for ZX81 were dreaded to fall out, but I think it was due to their physical appearance. Actually, I think a C64 cartridge will be more unsteady than a VIC-20 one.

As I wrote earlier in this thread, if you're going to install something internally in your VIC, I suggest the expansion board before piggy-backing RAM chips (if you can find them - the first revision VIC uses 0.5K chips and the CR revision uses 2K chips IIRC).