the science & technology of Commodore 8 bit computers and circuits

Disk drives, Monitors, SuperCPU etc.
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eslapion
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the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

I don't know if hardware is the adequate section to post this - perhaps "chit chat" would have been just as good but here i would like to share some of my experience and knowledge with people who are curious and want to learn about what I know of the science and technology behind Commodore 64, VIC-20, C128 and PET computers circuits. Just so you know, Skoe knows incredibly more than I do.

Of course, I can begin with what I learned about the PLA and how PLAnkton came to exist but the PLA is only one among many possible subjects to discuss.

I have to admit Tachyon and the CCC is the main motivation behind this series of posts I would like to do. I hope many things I will post here ends up on the Commodore Community Consortium.

I strongly encourage everyone to ask questions about the discussed subjects. There's a lot of stuff I'd like to mention but its easy to overlook things which may be important.

Just so everyone knows, I got a VIC-20 2 years before getting a 64 and this is where I began the learning process.

I got my VIC-20 in late 1983, my 64 in the summer of 1985 and moved on to the Amiga only around 1989. I purchased my last "new" Commodore computer in 1992 (an Amiga 3000/25) and ceased using it only in 1995.

Today I have two VIC-20s, 3 C64, one C128, an Amiga 1000 and an Amiga 3000, none of which are my original machines. I reacquired a VIC-20 around 1990, reacquired a C64 in 1998 (by virtue of the trade of an SX-64 with Gyro Gearloose), reacquired more C64 from Jean-Claude Lachapelle around 2006-2007 and got my first C128 from him too around the same time. I bought another A3000 in 2007 and got it fitted with a Mercury 35MHz accelerator.

So... what should we discuss first?


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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

When I got my VIC-20 back in 1983, the first thing I wanted to do was to understand how it works so I could copy and play all the games.

Cartridge games were the most impressive and fun to play.

They were copy protected solely by virtue of technical complexity. The first thing I discovered is that autostart games never use the BLK2 area ($4000-$5FFF). Sure the Scott Adams games use this area but they are not autostart.

Combine this with the fact that the original VICMON software from Commodore would not allow saving data above $7FFF and you've got a nasty all-in-one solution.

Jean-Francois Lefebvre of the Sorel VIC-20 computer club showed me how to alter 16k RAM expansion VIC-1111 with a DPDT switch that would serve a double function. It would swap the second 8k RAM block between BLK2 and BLK5 and it would render the expander "read-only" by disconnecting the VR-W line when set to BLK5. Another 3 pin switch would be added to toggle the first 8k RAM block between BLK1 and BLK3.

When dumping a cart, we'd wire the BLK5 line of the cart to BLK2. This would prevent the cart from starting and permit VICMON to save the data. Other than the special Scott Adams games which start with an SYS command, all 16k autostart cartridge games on the VIC either use BLK1 and BLK5 or BLK3 and BLK5. Since the data for BLK5 ended up in BLK2, you'd save BLK1 and 2 or BLK2 and 3 in one shot.

This had the wonderful effect of allowing us to make all VIC-20 16k games into a single file even if they use 2 separate memory areas.
Knowing what areas were used by a specific games, you'd set the second switch to BLK2 and the first one to BLK1 or 3, load the 16k file with the data destined for BLK5 going into BLK2, flip the second switch, type SYS64802 and bingo! Your favorite game starts.

Of course the drawback is that a 16k software takes a LONG time to load from a dataset at normal speed. We didn't have Turbotape back then.

Basic V4 is among the few pieces of software JF Lefebvre gave me back in 1983 and nobody else had even in 2006 when I got in touch with Schema.

I was a poor boy and couldn't afford a C64 so in 1984, while everyone was moving on to the 64, I was building a collection of more than 200 softwares on my VIC-20 and even starting to do deep electronic stuff with it. I didn't see my VIC as valuable at all back then and I experimented with it... a LOT.

In early 1985 I moved to Montreal and I discovered Addison Electronics and the case of my poor VIC took a serious beating as I drilled holes for reset buttons, freeze switch and other mods. About 5 months later, I got my C64... but no disk drive. I used the same datasette as with the VIC, fortunately there was Turbotape at this point.
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by dudz »

you didnt just desolder the ROM and read it out in some adapter or burner? that was common business here since the atari VCS era (where you have no other choice anyway)
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

@Dudz
No such trouble. JFL had a Ramax with 2 slots. One slot was modded to have the BLK5 line from the female connector wired to the BLK2 line of the Ramax's PCB.

The Ramax, on top of providing full expansion, became a universal cart dumping tool. I was 13 years old back then.
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by dudz »

i see ... i take it that cartridges with custom banking schemes were not common on vic20 then :)
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Re: the science & technology of Commodore 8 bit computers and circuits

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@dudz
Custom banking schemes is something I saw on the VIC-20 for the first time around 2007.

The machine vanished from the market in early 1985. The last "new" VIC-20 I saw was on store shelves of a Miracle Mart (they too vanished) in the spring of 1985 for 99$Can. At that point, cartridge games were liquidated for 3$ each.

I would find one last interesting use for my VIC-20 in the fall of 1985. When I finally got myself a C64 - I played Activision's Decathlon a lot.

Instead of playing "joystick jiggle" to get good scores, I would write a simple basic program that signals on the user port and made a simple interface from the VIC's user port to the 64's joystick port.

I think you can guess the rest.
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

Here is some of the history and people behind the 82S100.

http://www.computerhistory.org/semicond ... 8-PAL.html
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

@Gyro
Hey! Ironhat! Nice to see you here.

Actually, the person who informed me that it was not a good idea to mix TTL-LS technology chips with standard HC chips is Mr. Gearloose himself.

I think one of your former employers lost a lot of money because they made a mistake like that - they wouldn't listen to you. They had big problems because of that IIRC.
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

I've been lurking on REMOVED and following your debacles, it's better than any soap opera I've seen. When can I get season 1 on DVD?
The price one pays for pursuing any profession, or calling, is an intimate knowledge of its ugly side.
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

@Gyro:
Well, season 2 begins with me selling in excess of 230 U17 PLAnkton chips that turn out to be the perfect replacement for Commodore's 82S100 and MOS 906114-01.

'-)

More in development...
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
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