VIC 20 cartridge expansion board schematics?

[garry68]

Hello all,

I just wanted to ask if anybody knows of any schematics or PCB layouts to build a multi port cartridge expansion board for the VIC?

I have a few cartradged I would like to keep permanantly attached and switchable, but these boards seem to be relatively rare and can be quite expensive on ebay!
It dosn't look like it should be a very hard thing to build.

[Mike]

It dosn't look like it should be a very hard thing to build.

On a first approximation, it looks easy. After all, what's difficult about doing a 1:1 connection for most signals?

The rub's in the detail. Many cheap cartridge expanders only switch the +5V supply line, which is not a good idea - this opens up all scenarios of undefined behaviour from those chips missing the supply voltage up to possibly damaging them. We had discussed that here in Denial not too long ago.

The necessary refinement includes SPDT switches on all relevant select signals (/BLKx, /RAMx, /I/Ox), with pull-ups for all deactivated signals. There's also the Y line (audio in on later VICs), which is misused by some cartridges and which you might want to disconnect for cartridges that do not explicitly use Y for audio in. With three or more cartridge slots, it might also be sensible to buffer the address and data lines.

Finally, the schematics are one thing. The mechanics are also important: on the computer's side, the length of the PCB to cover the depth of the cartridge port, some room between the cartridges and also to the left and right to take the cartridge cases into account.

Quite some years ago, Jim Brain did such a design and got across practically all problems in the book. See here.

[chysn]

Aside from the technical issues, where on earth can we source the 22-pin female edge connectors with the correct spacing? The user port connectors are readily available, probably due to their use with other (more... ahem... popular) Commodore machines. But the cartridge ones aren't so easy to find.

[srowe]

Aside from the technical issues, where on earth can we source the 22-pin female edge connectors with the correct spacing? The user port connectors are readily available, probably due to their use with other (more... ahem... popular) Commodore machines. But the cartridge ones aren't so easy to find.

They're easy enough to source from China, they're the same as JAMMA connectors used in old game consoles. Google for "506 series edge connector 44pin". I do have concerns about the quality of them though, they seem "harsh" and may damage the edge connector on vintage cartridges.

[chysn]

They're easy enough to source from China, they're the same as JAMMA connectors used in old game consoles. Google for "506 series edge connector 44pin". I do have concerns about the quality of them though, they seem "harsh" and may damage the edge connector on vintage cartridges.

Thank you, I might try a project like this in the near future.

Who wins if there's a 35KB RAM cartridge in one slot, and a 2764 at block 5?

[Lechuck]

Aside from the technical issues, where on earth can we source the 22-pin female edge connectors with the correct spacing? The user port connectors are readily available, probably due to their use with other (more... ahem... popular) Commodore machines. But the cartridge ones aren't so easy to find.

I have recently built a 'Vicky Twenty':



I ordered all the components, including the connectors, to 'Run Stop Re-store' (www.runstoprestore.nl'). Cartridge connector label refers to web www.sullinscorp.com. Looking in that web for the connector ID (it is printed in the connector) I reach:

https://www.sullinscorp.com/product/?pn ... &toggle=in

Quality looks OK (at least the Vicky Twenty works very well, including the cartrdiges port). So, I guess you could order the connector directly from that 'Sullinscorp' web.

Cheers

[Mike]

Who wins if there's a 35KB RAM cartridge in one slot, and a 2764 at block 5?

Both lose. See here.

[chysn]

Who wins if there's a 35KB RAM cartridge in one slot, and a 2764 at block 5?

Both lose. See here.

[Mike]

[doug_in_nc]

If you do decide to build one, be careful that you use a PCB layout that doesn't allow you to swap cartridges in and out just by turning the 5V line on and off (looking at you HEScard 20), as those can damage cartridges as well an have unpredictable behavior. As an example, on the HEScard I found that if you use a Penultimate Plus in one, turning it off causes the VIC to boot to the normal prompt rather than the Penultimate Plus menu, but with the expansion RAM from the cartridge active. You need a design that switches the block select lines instead. Both the CardBoard 6 and CardBoard 3S do that, for example.

[JonBrawn]

Instead? Or as well?

[doug_in_nc]

Looking at the tracks on my Cardboard /6 I would say just the block lines. The GND and 5V lines don't appear to be switched.
I only picked up the board recently, and hadn't got round to using it in anger, but just noticed it has been "improved" by having a couple of traces cut, so once I repair them, I can check for certain.

[garry68]

Thanks for all the info on this, not as straightforward as it looks then.
I may look at ether buying or making one after christmas.

[Orangeman96]

FWIW: Schematic - VC/VIC 1020. -OGM