Mar 10, 2025
A discussion with @the-technicolor-whiscash reminded me of this awesome video talking about Don Eyles discussing the Apollo Guidance Computer
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A discussion with @the-technicolor-whiscash reminded me of this awesome video talking about Don Eyles discussing the Apollo Guidance Computer
I will be at Vintage Computer Festival East XIII this weekend! And so will the Cactus!
Stop by my exhibit, if you’re there. Just look for the guy in the derby.
The Cactus won Best In Show at VCF East XIII.
It tied with the exhibit combining the Altair 8800 & IMSAI 8080 computers with Cromemco Dazzler & Cromemco Cyclops equipment. Considering just how much work Bill Sudbrink put into recreating the lost hardware of the Cyclops camera, I can safely say he earned it.
My prize was a Corsham KIM-1 Clone Rev 2, generously provided by Bob Applegate of Corsham Technologies. Thank you, Bob! The KIM-1 just so happens to be what most folks consider to be the common bare-bones machine for the 6502.
Jason Scott of the Internet Archive & textfiles.com took some photos of the event. A few ended up on twitter, but you can view the album here.
I’ve got people asking me when the Cactus kit is coming out... uhhhhhhhh, one step at a time. I’ve still got plenty of work to do before we’re ready for that.
The Cactus, clocked externally at an incredibly slow rate.
You can see the individual CPU actions as they happen! Every address visit, every memory write -- all of it.
Today was great...
The Cactus at Vintage Computer Festival East XIII
What a fun weekend! I exhibited the Cactus, explaining why I built it, what motivations lead to its design choices, and where the project was headed next.
Folks were welcome to come by, try their hand at using the front panel interface, type in a program in BASIC, or just listen to me ramble for awhile. The Cactus performed flawlessly all weekend long, surprising the hell outta me. Meanwhile, my Heathkit H89 (which was being used as a terminal) blew 3 fuses as a result of heavy operation. Turns out I was using fast-blow fuses that were rated too low.
I tried various experiments, like clocking down the 6502 to incredibly low speeds, well below the normal ~100KHz threshold. A special thank you to
@aperture-in-the-multiverse
for helping me with my exhibit. He hooked up my Epson LX-300+ dot matrix printer to simultaneously print whatever was being typed on the terminal. He also used my Libretto 70CT to copy over Lunar Lander via Hyper Terminal to give folks a fun game to play. My exhibit was directly adjacent to one with an Altair 8800B & IMSAI 8080, allowing for a good design contrast between my work and the style of design I was being influenced by.
VCF East XIII Approaches
Vintage Computer Festival East XIII is a week away.
Come see the Cactus! It will be on display both Saturday the 19th & Sunday the 20th. This is what I’ve been building up to for quite some time now. And it seems I will make it -- the Cactus is operational, but it is far from finished.
I hope to see you there!
It works.
The Cactus now can run instructions from EPROM or entered into RAM via the front panel toggle switches. Not only that, it can run BASIC!
The R/W line has signal contention caused by the data control card not allowing the CPU to write back to memory. I rearranged some wires on the status control card, hoping to fix the issue and that did fix the issue of R/W not going low. However, there was alot of ringing on that signal line, as shown by the oscilloscope image. I added in a tri-state buffer that would go high-Z when the machine was set to RUN (and thus the 6502 was in charge). I also moved the pull-down segment around, and all the sudden, the CPU could write to memory. A test program showed that it could even run a simple program that deposited a value at a specific address.
I didn’t believe it. So I tried another program, this time toggled into RAM by hand, and it ran fine. Then I changed the values around, and it once again did what it was supposed to. I tried one more program, and... sure enough, memory was changing correctly.
So I played around with it for a bit before socketing the OSI BASIC EPROM and trying to run it through the serial line. It took a few attempts before I saw text. It responded to keyboard input, but it would incorrectly calculate available RAM before going into a loop. A few more experiments later, and I realized I could manually tell it 32K of RAM was available. Running programs in BASIC is feasible!
The Cactus is going to be ready for Vintage Computer Festival East XIII