#6502

[commodorez]

At VCF East XX, former Commodore engineer Bil Herd gave me a handful of old chips from his storage bins. These are mostly 6502 family parts, meaning I'll find uses for them in my various projects. Those two in the middle that say SAMPLE and PROTOTYPE are the coolest of the bunch, and I'm gonna put these to work. Thanks, Bil!

[adafruit]

🎄💾🗓️ Day 3: Retrocomputing Advent Calendar presents the Commodore VIC-20! 🎄💾🗓️

The VIC-20 ⌨️📺🕹️, released in 1980 by Commodore, was the first computer to sell over a million units. It had a 6502 CPU running at 1 MHz, 5 KB of RAM (expandable), and displayed up to 22 characters per line on a color-capable screen. An affordable and friendly computer, the VIC-20 was great at games and basic programming and was supported by a library of software and peripherals. It connected to TVs for display and included Commodore's BASIC interpreter for programming. Its success allowed other computers like the Commodore 64 to make its mark.

And since this is a #firstcomputer celebration here's a fantastic story from Jeff -

My first home computer was the Commodore VIC-20. I must have been in second grade (1986/1987). My Dad was working somewhere away from home, but one weekend Mom drove us two kids to spend the night at the motel that was his home base.

He had bought this computer, the VIC-20, and hooked it up to the hotel TV. I remember entering the program pictured below (probably Mom typed it in, actually) and being blown away by the birds flapping their wings across the screen.

The other distinct memory I have is the next morning my folks woke me up and asked whether I was hungry. No, I very much wanted to play with the VIC-20, so I made up the most obvious word that came to mind: "No, I'm Vic-y". I think they were very puzzled. We probably went and had breakfast regardless of whether we wanted to see the birds flying again.

Check out the wikipedia page for some great history, photos (pictured here), and more -

VIC-20 - Wikipedia

And the COMMODORE vic-20 commercial commercial compilation, featuring William Shatner.

Have first computer memories? Post’em up in the comments, or post yours on socialz’ and tag them #firstcomputer #retrocomputing - See you back here tomorrow!

[verilog-official]

the genius (stupidity) behind the FPGA in my 6502 computer has almost everything to do with the clock.

basically, the FPGA has a 12mhz clock input, and an adjustable clock output which goes to the CPU.

with the 12mhz FPGA clock, the CPU can run up to 6mhz. however, since the 6502 uses a synchronous bus, all the other devices on the bus must be able to run at that speed as well. and, well, they can't.

my solution was to dynamically adjust the clocking for each peripheral on the bus when it's being accessed. the FPGA monitors the address bus, and when the CPU selects something that runs slower, such as the EEPROM, it halts the clock for a little bit until the EEPROM can catch up.

this allows me to put other stuff on the bus too, like the LCD controller. in the original Ben Eater design, the LCD was attached through the VIA (essentially a GPIO controller). since the nature of the LCD controller needing to constantly switch between reading and writing, this made a pretty sizable overhead. by putting it on the bus directly, not only do we free up 7 GPIO pins, we also significantly reduce the time it takes for something to be written to the screen.

there's was problem though; I plan on using the VIA's timer functionality which essentially just counts clock cycles. if the clock constantly changes speed, this number will be useless. so, the FPGA generates two clocks, a monotonic clock for the VIA, and a non-monotonic clock for everything else.

but the VIA also needs to be synced with the CPU in order for them to communicate. so, when the FPGA sees that the CPU wants to access the VIA, it synchronizes their clocks for a short moment, then essentially "connects" them together for one cycle, before reverting to their original clocks.

this way, the VIA can properly keep time, and the CPU can change its speed at any time. additionally, since the VIA has its own clock, you can adjust it independently and slow it down if you need to track long periods of time, or speed it up if you need more precision.

oh and I forgot to mention that the CPU can also adjust it's clock speed, but i don't think it would make much sense to do anything but the top speed.

[smbhax]

Oric Atmos - Electronic Soundmaker & Computer Music - May 1984

[cerulity]

About Me

thought i would make this post because why not

My professional online pseudonym is Cerulity32K, or Cerulity. Though, my preferred name is Kali, and my username for personal accounts is Kali the Catgirl.

Though my mental conditions are mild, I do have ADHD (inattentive) and am seeking an autism evaluation. I am also trans (she/they).

But let's get to the good stuff. I excel in computing, especially low-level stuff and graphics (webdev scares me) and math, advanced functions, calculus and linear algebra being the most useful to me. I like to intersect math and computing, and it leads to some pretty fun results, especially when dealing with graphics. My main languages are Rust, C, C++, C#, and Zig, and I know a few architectures (x86_64, RV32E, 6502, and my own that I'm working on). Vulkan is by far my favourite graphics API, and I've built a few things on top of it including (multiple times) a terminal animation framework.

I also do music. My favourite types of music are on the two extremes of electronic. FREE.99 and Femtanyl are my favourite artists on the loud and distorted side, but on the calmer side I enjoy Creo and Solarstone. I also make music myself. I've made a few original songs, and many remixes. I specialize in industrial chiptune and what I like to call "rustcore". My two music environments are Waveform and Furnace, though I am trying to make a tracker of my own using Pommel, my own synthesis library.

My favourite game genres are automation, puzzle, and platformer. Mindustry, Factorio, Exapunks, and Celeste are my favourites.

I'm learning to do pixel art (that's where my pfp comes from), and I'm planning on PNGtubing eventually. One day I hope to be able to translate my avatar into a 3D model.

All in all, I'm just a software catgirl :3

[xfce-official]

are there any decent hand-assembleable computer kits out there? like, 6502 or Z80 based systems that provide parts and pcb unassembled. i want to mess with simpler computers but also don't want to buy an expensive 45 year old machine. looking at the ben eater breadboard system but that's breadboarded so idk if i'd enjoy the assembly as much

[techav]

Stepping Backwards a Bit (or 24)

I was looking for a simpler project. My recent 68030 work has been challenging and really pushing the limits of what I can do. I wanted something I could work on, but perhaps where someone else has already worked out the hardest parts.

I find laying out PCBs to be rather relaxing. It's one of those repetitive, almost meditative tasks, like needlepoint or whittling. The kind of hobby where I can turn on some music or a comfortable old TV show, zone out for a few hours, and wake up to this new thing that I created.

Debugging however is very mentally taxing, and the design work required to have a functional schematic to create a PCB for is an active whole-mind prices. So what I really needed was an existing project I could design a board for.

Enter [Grant Searle]. If you're not familiar with [Grant Searle], he has excellent designs for breadboard computers with a very minimal parts count. I studied his minimal Z80 design when I was first starting to build my own computers and learned a lot from it. I highly recommend his work for anyone who is interested in learning how to build their own computer but doesn't know where to start.

I was recently given a Rockwell 6502 CPU pulled from a dead LED marquee. I've never actually worked with 6502, so this seemed like a good time to try building Grant's 8-chip (or 7-chip) 6502 computer.

A few hours later, I had a PCB design completed, gerbers generated, and an order placed. Less than $5 for 5 boards, including shipping. A couple weeks later they arrived in the mail.

I did end up making a few modifications to [Grant]'s design. Instead of a clock circuit made from a discrete crystal and a couple inverter gates, I used a TTL oscillator because I've always found them to be more reliable. I also added support for an FTDI USB Serial adapter chip so that the board can be used with a modern computer as a terminal. And finally, since a PCB is much harder to add new components to relative to a solderless breadboard, I added an expansion header. All of it wrapped up in a compact PCB with lots of helpful silkscreen marking.

I realized after I had ordered the PCBs that the 16kB ROM chips [Grant] used are no longer manufactured or readily available. I have plenty of 8kB EEPROM chips on hand however. Thankfully the OSI BASIC interpreter [Grant] ported to this design fits within 8kB, so I was able to make a few adjustments and re-assemble it to work with the ROM chips I have on hand.

After a small glitch with my EEPROM programmer, it works!

It's quite a change going from my 33MHz+ 68030 to this tiny 6502 running at just under 2MHz. The BASIC text-based Mandelbrot renderer that completes in seconds on my 68030 takes four and a half minutes on the 6502. Not bad at all, considering my bus-impaired 68000 build takes 9 minutes to do the same.

This was a fun little project. It was a nice little break from some of the more difficult projects I've been working on. I have shared the project on GitHub for anyone who might want to take a look.

I hope to have this project with me this weekend, June 14-16, 2024 at Vintage Computer Festival Southwest. I'll be at table 207 in the Tandy Assemble hall, just across the street from the main exhibit hall.

[meg4de5tr0yer666]