Hacking Vic-20 cartridges

yoyodyne · Post by **yoyodyne** » Wed Mar 09, 2005 12:33 pm

Hi, I was wondering which (if any) common vic-20 carts may
have EPROMs in them, instead of roms. A socket would be
even better.
On the 64 side, I have found that the Mach 5 disk utility
cart is nice. It has an 8k socketed EPROM that is easily removed,
reprogrammed and re-installed. Or, even better, replaced with
a 64k (or larger) EPROM and a selector switch.

I would like to try this with the vic. If anyone has any info
about this, please let me know!

Thanks,
Brian

Schema · Post by **Schema** » Wed Mar 09, 2005 2:48 pm

As it happens, 6502dude is (hopefully) going to be showing us how to do this at the next TPUG meeting here in Toronto.

For the C64, you don't have to butcher old cartridges - Alphaworks sells new, blank cartridge PCB's. http://www.alphaworks.com.au/store.htm

It would be great if there was an equivalent for the VIC-20!

6502dude · Post by **6502dude** » Wed Mar 09, 2005 3:32 pm

Some of the Vic-20 cartidges simply have a chip (blob) stuck to circuit board. Others have 24 DIP ROM chip.

Cartridges are pretty cheap, so it is simple to desolder DIP version of rom chip, insert a socket and you are ready for eprom insertion.

The ROM pinout is same as 2532 (4K) eprom. Cutting a couple of traces and wiring allows use of more standard 2732 Eproms.

One challenge is finding modern eprom burners that will work with eproms this small.

If you don't wish to hack up a Vic-20 cartridge, Rat Shack used to sell 44 pin edge card circuit boards that matched Vic-20 interface port. I think they may be discontinued now though. I have wired up one of these for use with 2764 (8K eproms) with such a board.

yoyodyne · Post by **yoyodyne** » Wed Mar 09, 2005 9:04 pm

Before anyone yells at me, no Vic-20 carts were harmed to
research this post tonight!

I found that my Submarine Commander (Thorn EMI) and
VIC Forth (HES) both have EPROMS inside, but are not socketed.

As for a modern eprom burner, I use this:

http://www.ustr.net/epromer5/index.shtml

I really like it. Works well with the older, smaller eproms I need
to use.

carlsson · Post by **carlsson** » Thu Mar 10, 2005 2:17 am

I would suppose only prototype carts and alike have chips in sockets? On the subject of creating new carts, I believe the VIC community has a standing invitation from the AtariAge community cart makers if we are unable to manufacture ourselves.

6502dude · Post by **6502dude** » Thu Mar 10, 2005 8:14 am

I haven't seen a cartridge yet that has uses sockets for Roms.

Sockets + ROM or Eprom + cartridge cover presents a bit of a physical clearance problem (it will not fit into Vic-20).

This is another reason to leave top cover off your hacked Vic-20 cartridge.

Plus, for manufacturers, using sockets just adds to production costs and would have provided hackers back then an easier option to pirate games.

I use Promenade for smaller Eproms. It will burn up to 27512 (64K). I once used it to burn a 27010 (128K) with socket adapter, but this was a bit of a PITA.

I have built a could of Eprom burners so I can do eproms from 2764 (8K) though to 29040 (512K flash eeproms), at much faster rate than Promenade.

carlsson · Post by **carlsson** » Thu Mar 10, 2005 9:40 am

Well, the casing doesn't have to be a flat box, it could be in two terraces of which the chip is mounted on the back end, something like this:

Code: Select all

        ___
  _____/   |
_|_________|

vic user · Post by **vic user** » Thu Mar 10, 2005 11:07 am

wow Anders, you did a perfect job drawing the cart. for the 40/80 column display

chris

6502dude · Post by **6502dude** » Thu Mar 10, 2005 12:21 pm

carlsson wrote:Well, the casing doesn't have to be a flat box, it could be in two terraces of which the chip is mounted on the back end, something like this:
Code: Select all
        ___
  _____/   |
_|_________|

Nice pic!!!

The height issue is with modification of exiting cart. ROM chip on cartridges tend to near center of premade cartridges. Using 22 (A/B) edgecard project perfboard allows alot more flexibility where you locate eprom for CRT ROM image hacking.

carlsson · Post by **carlsson** » Thu Mar 10, 2005 5:05 pm

Ah, so the idea would be to solder away the ROM chip and put a socket plus something into it. Yes, in that case I can agree if it gets tight, although the circuit design may differ a little on different cartridges (and you want one which has all or as many pins as possible connected).

6502dude · Post by **6502dude** » Thu Mar 10, 2005 10:21 pm

Here are some pictures on Vic-20 cartridge hacking

(a) Bottom of case - note location of screw and 2 slots at top of image which have clips to release top & bottom of case

http://www.bjlyons.com/cbm/vic-20/4kbotcase.jpg

(b) Bottom of circuit board - 2 traces cut and 2 wires added to modify for use with 2732 Eproms (I'll bet somebody can tell what was orginally in this case based on number sticker on board)

http://www.bjlyons.com/cbm/vic-20/4kbotcct.jpg

(c) Case with circuit board. I orginally used 2532 then modified and made note on case. Note socket installed in place where ROM was.

http://www.bjlyons.com/cbm/vic-20/4ktopsocket.jpg

(d) As above in (c) but with 2732 Eprom installed in socket

http://www.bjlyons.com/cbm/vic-20/4ktopeprom.jpg

(e) 8K board I quickly put together a long while ago to test 8K ROM images. No special address decoding. I may change to 27256, add some address code logic and add real time clock chip (just need the spare time)

http://www.bjlyons.com/cbm/vic-20/8ktop.jpg

(f) As above in (e) bottom of circuit board

http://www.bjlyons.com/cbm/vic-20/8kbotcct.jpg

Cheers!

Schema · Post by **Schema** » Mon Mar 21, 2005 9:01 am

6502dude wrote:Here are some pictures on Vic-20 cartridge hacking

Excellent, thanks again.

I made the same changes to one of my carts (Mole attack, I have several copies) and added a socket, and it works perfectly! The Hesmon ROM you gave me works fine.

Where does the 4K on the ROM show up in the VIC's memory again?

tlr · Post by **tlr** » Mon Mar 21, 2005 10:26 am

Schema wrote:Where does the 4K on the ROM show up in the VIC's memory again?

If it autostarts: $a000-$afff.
The same data could show up as mirror images in other places aswell (like $b000-$bfff), but $a000-$afff is the primary place.
The kernal reset routine at $fd22 will to an indirect jump to ($a000) when a rom is identified.

aneurysm · Post by **aneurysm** » Sat Apr 02, 2005 3:10 am

damn
i should get off my ass and figure out how to make a hesmon cartridge

6502dude · Post by **6502dude** » Sat Apr 02, 2005 11:18 am

aneurysm wrote:damn
make a hesmon cartridge

Don't do it just for Hesmon (because it sucks).

I use built in monitor within C128 when doing 6502 stuff on CBM equipment.