Denial

Hi everyone,

Recently I picked up this interesting looking cartridge, mainly as it had the Mr Micro logo on it. Originally from the ebay auction picture, it looked like it might be a C64 based cart - but upon arrival I found it was a Vic 20 cart (Or at least has the same amount of pins).



I tried plugging it in, but nothing happens (Even with another cartridge plugged into the expansion part at the back). I guess it might need a SYS call to get it going.

But any ideas what it might be?... I wondered if it was some kind of cartridge backup system due to the expansion part. Never seen any adverts in the old magazines from Mr Chip, apart from their games.

What's the underside like? Does it have anything interesting on it?

It's got a bit of black (leathery) tape over the back of the pins. No chips or anything like that.

The four contacts in the middle would address BLK 1..3, and BLK 5.

But they aren't connected, but the ones left two them - addressing RAM 1..3 - are, and these lines go to two TTL's.

I'd assume, that this adapter cart maps the some of BLK address range of ordinary carts into the $0400 .. $0FFF range. You could try whether an 8K RAM expander shows up as 3K RAM expander, with that adapter in-between.

Greetings,

Michael

I have a vague memory we have seen and discussed similar cartridges before. Mike's suggestion is good. Another suggestion is that a regular 8K memory expansion may get relocated to $A000, which means you could use it to play cartridge dumps without a switchable 32K cartridge.

Thanks Mike - i'll give that a try when I next get chance. Will a Vixen multi-ram cart set to 8k be sufficient for a test?

fgasking wrote:Thanks Mike - i'll give that a try when I next get chance. Will a Vixen multi-ram cart set to 8k be sufficient for a test?

It should be. Afaik all 8k carts look the same to the VIC 20.

Seems strange that pin 2 (from the left), which is PWR, would be so small. I'd love to see a backside scan, to see where the wires go.

Jim

Right, I used a Vixen cart set to 8k .. giving 12xxx bytes free etc and plugged that in. This time I got something different - just a black/blank screen when switched on. So it seems to have triggered something.

Pressed some keys, joystick buttons etc - but nothing though.

As requested, here is the back with the tape removed. Hopefully this might help shed some light. Glad I picked this up in the end (Only because of Mr Micro logo did it pique my interest).

I reverse engineered it. It appears to map an 8K RAM cart at BLK1 into RAM-RAM3. But, since BLK1 is only 8kB, it maps RAM2 and RAM3 into the same 4kB bank, as far as I can see.

Strangely, the dual TTL ICs seema waste. They are 70LS00 units, as far as I can tell from the reverse engineering. But, the outputs are all negated with second 74LS00 units wired as inverters. A single '08 would have done the same job.

Schematic at: http://www.jbrain.com/vicug/gallery/misc/Mr_Micro

Jim

brain wrote:I reverse engineered it. It appears to map an 8K RAM cart at BLK1 into RAM-RAM3. But, since BLK1 is only 8kB, it maps RAM2 and RAM3 into the same 4kB bank, as far as I can see.

Strangely, the dual TTL ICs seema waste. They are 70LS00 units, as far as I can tell from the reverse engineering. But, the outputs are all negated with second 74LS00 units wired as inverters. A single '08 would have done the same job.

Schematic at: http://www.jbrain.com/vicug/gallery/misc/Mr_Micro

Jim

Hi Jim,

Could you tell us what software you use to generate your schematics?

Thank you

Gabriel Angelos wrote: Hi Jim,

Could you tell us what software you use to generate your schematics?

Thank you

EAGLE: www.cadsoftusa.com

If I am doing rev-engr, I also use PhotoImpact to mirror the back PCB and lay it over the top at 50% transparency, which makes it easier to rev-engr.

Jim

brain wrote:EAGLE: www.cadsoftusa.com

If I am doing rev-engr, I also use PhotoImpact to mirror the back PCB and lay it over the top at 50% transparency, which makes it easier to rev-engr.

Jim

Thanks Jim!

Found what it is!! .... Searching through the Home Computer Weekly scans when I found this:

The "Ramdam"

http://gtw64.retro-net.de/vicscans/ramdam.jpg

Seems to match what people have found.

The advert mentions a memory test program and a "MicroVaders" game that comes with it. I suspect its a tape (Which sadly I don't have), but wonder alternatively by chance if the game "MicroVaders" could be hidden away on the cartridge and accessible via a SYS call? (Any that I can try?)

There is no game hidden away on the cartridge.

The cartridge you have physically remaps a 16K ram pack to act as if it is a 3K expansion.

This allows you to play something like Skyhawk 3K version on a Vic20 with 8k or 16K expansion without having to buy a separate 3K cartridge.

The games mentioned would have come on tape or maybe a listing as an enticement to buy it. There is nowhere to store them on those logic chips on the cartridge.

I checked GameBase V2 and the game by Mr Micro called Microvaders and Memory test utility are not listed....yet.