the science & technology of Commodore 8 bit computers and circuits

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

Post by Tachyon »

I'll do what I can to copy relevant info to the CCC, though I also encourage people to join and actively participate.
The prime purpose of the CCC is active, interactive, and live collaboration between those with information to share and those with projects to complete.


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

Post by Gyro Gearloose »

@Eslapion: Not bad. I'm just a bit sad you didn't keep the name PLAtypus.

Anyways... My first "hack" on the VIC-20 came from not having any games. A neighbor had Omega Race so I borrowed it. I ran home and was so excited I jammed the cartridge in at an angle, turned on the VIC to be greeted by the READY prompt. So I jammed the cartridge in with the power on and noticed nothing changed and the VIC didn't crash. So I turned the thing off and on and played the game.

A bit later someone in Rimouski also had a VIC-20 and photocopied an article in 73 magazine (hams!) on how to make a 24K expander for the VIC. This was an insane proposition and I nearly lost my mind.

I think I still have the photocopies somewhere. Here's a text archive, which apparently was OCRed with a VIC-20 too:

https://archive.org/stream/73-magazine- ... 5_djvu.txt

Anyhow, I spent the summer collecting empty bottles in the trash for money, eventually I made 40$, and even got injured once from broken glass. I still have a scar on my toe. 40$ was enough to buy 2 8kx8 SRAMs. I already had a little electronics workbench dedicated to the disassembly of TVs (and much smashing of tubes) I got in the trash and blowing up LEDs (another story!*).

I modified the plan slightly, I stacked the chips instead of wiring them out individually, and I whacked it together and it worked. This allowed me to type in more games from magazines and stuff. I also worked at the community center so I could buy those super-tempting Compute VIC books. Eventually I learned about assembly and the KERNAL.

Then I remembered the cartridge incident and after some trial and error I was able to get it to work again and I could "see" the cartridge contents. From there, it didn't take too long to figure out the same trick everyone else did for the banks and I got Omega Race to work on my expansion.

*OK, here's the story. The library had serious electronics textbooks, one of them was about lasers. The book talked about laser diodes, the schematic symbol looked the same as a regular LED so I thought it's worth a try with a regular LED, especially since magazines at the time were peddling "simulated lasers" with LEDs. I either built it wrong or 1970s laser diodes needed serious pumping, but that LED exploded instantly with the top flying off like a pellet. The smell was also quite remarkable.

Anyhow, I found scans of the photocopies:

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

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Gyro Gearloose wrote:@Eslapion: Not bad. I'm just a bit sad you didn't keep the name PLAtypus.
PLAtypus was supposed to be a PLA replacement based on Atmel's AT27C020 PROM with jumper settings to select between PLA replacement for the C64, C16 and 1551 drive. I even got a special logo drawn inspired by the picture you sent me.

Unfortunately, it turns out all Atmel PROMs generate glitches when there are changes on the input values which should not cause any changes on the output. In combinatorial logic, we call these "don't care". Unfortunately, there is no such thing as a "don't care" for memory chips; all changes on input causes the chip to look up for the new value to output in its table.

The ST M27C512-90B6 will not cause glitches significant enough to be detectable in the digital world. Unfortunately, almost all chips with this part no. you can find on eBay now are actually rebranded Winbond PROMs which do generate glitches.

Since Fredric created the VHDL code for PLAnkton which is based on a completely different chip, he's the one who chose the name.

I gotta tell you... other products from the same family are in development. You think you could make a contribution? I need a good VHDL coder right now. Fredric is busy with other stuff.

Concerning your VIC expansion, inspired by your expander based on 3 x SRAM chips of 8k x 8, I remember asking you to mod a VIC-1110 to carry 32k. I did the same thing again 6 months ago for a young Commodore collector and this time I took a photo of my work and got it posted on Denial's VIC-20 Wiki.

Here:
http://sleepingelephant.com/denial/wiki ... 2k_mod.jpg
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Gyro Gearloose
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

The XC9536 is NRND. What family are you referring to? Looks like Xilinx dropped the whole XC9500-XL family.

I've designed a few trinkets for my Commodore junk, but I learned to keep things to myself years ago. Here's a nice little switcher I made earlier this year.

Image

Image

Years ago I decided to see how easily I could make a replacement SX-64 keyboard cable. People argued with me about printer cables fitting into the SX-64's belly. They don't. The SX connectors are non-standard sized and there's a notch. People still argued. I made this:

Image

It looks OK, it fits, it has pull tabs to easily remove the cable, it folds up and fits in the compartment.

But people are happy buying this:

http://www.ebay.com/itm/COMMODORE-SX-64 ... SwuMFUkfVr
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eslapion
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

Gyro Gearloose wrote:The XC9536 is NRND. What family are you referring to? Looks like Xilinx dropped the whole XC9500-XL family.
The XC9536 is discontinued but not the XC95xxXL AFAIK.

Digikey still has a few thousands in stock:
http://www.digikey.ca/product-search/en ... ageSize=25

I usually buy them in racks of 160 units. In 2012 Xilinx issued a discontinuation notice but then apparently issued a retraction due to customers demand. Anyways, AVNET also stocks them by the thousands.

Impressive little switcher integrated in a TO-3 form factor you got there. Elegant solution to reduce the heat.

I elected to do away with bridges and TO-3s altogether in my own VIC-1541 (12" board) and standard 1541. However, if you could spare one of these switchers of yours, I'd love to put something like that in my old VIC-20 with PET style keyboard on which I try as much as possible to retain the vintage appearance both inside and outside but try to explore avenues to stretch its lifespan. Its already nearing 35 years of age and still operational like new!
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Gyro Gearloose
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

Ah yes, the XC9500 family is obsolete, not the XL stuff. I guess I didn't look hard enough.

Hey, I do have a spare switcher PCB, but can you spot the fatal flaw that would make this switcher actually reduce the lifespan of your VIC?

Hint: It's not an unsolvable problem, just sort of makes the whole exercise moot. How much current does one of those VICs need?
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

@Gyro
The VIC with PET style keyboards draws about 1.1A on the regulated 5V and power trends used to make PT78ST205 regulators with similar components and surface - just not in TO-3 form. They have an excellent efficiency ratio and can deliver up to 2A.

What's wrong with yours?

Could you not just shove one of these on a TO-3 adapter board of yours?
https://www.digikey.ca/product-detail/e ... ND/2352134
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Gyro Gearloose
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

There's nothing wrong with my module, there's nothing wrong with the CUI, but there's still a fatal flaw.

Hint: it's in my picture of the 1541.

Maybe it's not so fatal, that's a bit dramatic. Nothing blew up in my tests so far, I need to look into it some more, but the number "35 years" has something to do with it too. I still think there's a long-term fatal flaw. Maybe you''ll guess it and can tell me what you think? :mrgreen:
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

@Gyro
I guess you need to replace the large capacitors too... which I did in my own PSK VIC. Is that the culprit?

It doesn't change the look very much other than the fact they are smaller.

If you replace the CPU, ROMs and VIAs with CMOS versions like I did then you can get away with even smaller capacitors. On my own 9" board 1541 (board 250442), the 5V load fell from 630mA to 280mA which also allows the usage of less powerful switchers.

If the problem is other than that then I just don't see.
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Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

You got it, the voltage on those big caps goes up. It doesn't matter what switcher you use.

But now you need less capacitance.

In fact, you can get away with a radial capacitor that's physically small enough that it fits on the module, sticking in the air. Just cut a leg on the the old caps, leave them in, and there you go.

Height limits apply of course.
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