With the Great Chip Shortage still delaying deliveries of new components, now might be a good time to look around your lab and inspect those piles of chips that you thought “might come in handy one day”. Chances are you’ll find a good stack of 74xx series logic, once ubiquitous but today mostly obsolete thanks to powerful microcontrollers and FPGAs. It would be a shame to let them go to waste, so why not use them to make a neat 1980s-style computer?
With this idea in mind, [Anders Nielsen] designed the ABN6502: a single-board computer based on the venerable 6502 processor, but with relatively modern interfaces like a VGA monitor output, a PS/2 keyboard connector and even a wireless module to simplify firmware uploads from a PC. One design requirement was to minimize the number of new components needed; the average hacker interested in building the ABN6502 will probably have many of the chips lying around somewhere in their workshop.
The component list reads like a typical bill of materials for a 6502-based computer, but comes with a lot of flexibility to allow for part subsititution. For the CPU, both the classic NMOS 6502 as well as the modern CMOS-based 65C02 are supported, along with their 6522 companion chip that provides I/O ports and timers. A ROM socket can hold either modern, fast flash chips or traditional but slow UV-erasable EPROMs.
Instead of using DRAM chips with their complicated refresh requirements, [Anders] went for 32 KB of SRAM to implement the main memory; unaffordable in the ’80s but easily available today. Standard 74xx series logic chips glue all the components together, again with several options to add or remove features as the user prefers. Pin headers bring out the I/O ports for easy connection to external peripherals.
The ABN6502’s software library is currently limited to a bootloader, but a complete development toolchain based on the CC65 compiler should make it easy to develop all kinds of programs on this platform. We’ve already featured the clever wireless ROM flashing system, as well as a demonstration of the 6502 driving RGB LEDs.
Every now and then, I look into my IC stash (i.e. spreadsheet), and think,
Hey! I have enough to build me an Olde Tyme Comfutre!
I’ve looked at OSHPark for those type of boards people have shared.
And as I delve deeper, I don’t have a few key components.
(sigh!)
Could be worse: You’ve got all parts, spend many hours designing and building, only to find out that one chip didn’t survive four decades in a drawer and you can’t get a replacement…
That’s me too frequently also… yay, looks like I’ve got all the parts to build X…. oh not quite, the Illudium Q36 space modulator driver needs a companion phase inverter buffer chip that I haven’t got, runs on +7 and -25 volts, and was EOLed in 1974…. ah, here’s one on eBay… $272 … looks like that’s a nope then.
Guys, please stop. You’re going to make me ger-manic-depressive! 😂
At least that can be cured with some OC71 black pills.
Haha, thanks. 😁
Btw, there’s a fascinating story about the ancient Germanium bipolar transistors by Philips.
In essence, the fillings were contaminated somehow (sabotage?), which caused some crystal growth inside the metal cans.
That made the OC17x transistors inoperable for RF (important to know if working with NOS parts).
A little electric shock (ground+collector? or ground+base?) could temporarily fix them, though.
https://www.elektormagazine.de/magazine/elektor-200807/3073
There was no sabotage with OC17x and AF11x, just tin whiskers (the case was made from tinned steel and not heated after forming). Can also be temporarily fixed by throwing them at the wall. (don’t forget to detach the radio first!)
Interesting. I never stumbled upon this problem with OC16* and OC17*. Most alloy transistors I dismantled had the system dipped either in epoxy or the whole can was filled with some kind of grease. Probably to stop moisture. But yeah, I have some transistors with whiskers growing out of the can.
Reading this makes me want to get out my old 486 Computer with EISA Buss and ATI video card! Many memories ♡
This gives me a bit of a prompt!
In my stash there are a couple of tubes of the Harris RTX2000 FORTH chips and I’ve thought of making a FORTH “Arduino”.
As well as them, there are close to 80 x 6511AQ chips and lots of others that we used in our industrial control stuff.
It is a pity to toss them so maybe I will get going on some boards….
Curious as to what you have, I did a DDG.
https://users.ece.cmu.edu/~koopman/stack_computers/sec4_5.html
https://hackaday.com/2018/02/22/forth-system-on-chip-takes-us-back-to-the-80s/
https://www.cpu-world.com/CPUs/6500/Rockwell-R6511Q.html
https://www.complang.tuwien.ac.at/anton/euroforth/ef04/pelc-bailey04.pdf
I’m curious if the posting engine will allow this many links…
We (DSPSystems) made a number of products for industrial control running FORTH on the 6511AQ chips. They are an enhanced 6502 with I/O on board. The 6505 in the post attracted me to this thread.
Later we changed to a Mitsubishi version as it was CMOS. Then on to PICs……..
My own (coodenco) products were PIC based.
All retired now other than making some Ham Radio bits and an occasional repair of some boards still running up to 30 years later. Pretty good I think :)
I do need to have a stock take and add items to my ebay store that I’ve recently started to save tossing these things away.
You wouldn’t be interested in selling one or two of the RTX2000 chips? That would be a lot of fun, building a little Forth machine.
I don’t know if this is allowed here but…
https://www.ebay.com.au/itm/304496845543
This link shows a couple of photos of the fruit imaging system we made. The RTX2000 was magically fast. A great chip.
Ah, dang. I was hoping you might be willing to sell one for a more “hobbyist-friendly” price, rather than the collectible prices they seem to go for. But I can’t blame you. :)
just out of interest, see Ebay’s other listing….
https://www.ebay.com.au/itm/393605689758?epid=21045800730&hash=item5ba4ba319e:g:7awAAOSwQslheBhC
I wonder if he has sold any?
I’ve just updated the ebay to include a socket!
Hi, I’m interested to try some Harris RTX Forth chip, I was wondering if I can buy one or two from your tubes?
Hi, do you still have some RTX2000 chip left?
holy shit, this article made me realize 74xx chips might go out of stock some day not far removed
Don’t worry, the 74xx was made by different manufacturers over the years.
And as long as people care, the 74’s will be around.
Surely, it must be possible to print them at home in a few years, once we have lithographic printers.
And while we’re at it, we can bring some pals from the 4000 series back, too!
Maybe we can print them on some sort of plastic sheet or glass, not sure.
Size is not much of an issue, after all.
If we do DIY, a die/core 10 times the size wouldn’t be an issue.
Maybe we will be making 555s at home by then.
A bright future is ahead of us! 😁
It’s glue, and so valuable that there have been an awful lot of variants to keep up with the times but which keep the numbering and some level of compatibility.
74S00, 74H00, 74C00, 74L00, 74LS00, 74HC00, and all the rest.
At least 55 years of it. RTL and DTL were almost a blink.
I have a z80 clone (64180) dating back to when Steve Ciarcia used one to build a SBC in a Magazine.
The magazine was lost years ago, but the chip is still here.
I have Steve’s HCS II boards (~150 blanks), some working HCS IIs and a few of Steve’s boards (BCC180, etc. ). :-)
I followed your link to HLA, but didn’t see any mention of the boards.
I’ll do a DDG for more info on the HCS II boards.
Ren, follow the link to my web site and click the email icon. Not sure where things are at the moment but I do have all the information (and even the DOS libraries for CircuitCellar’s HCS stuff). Some of it is a pain. Ed’s asm code is hard to assemble.
That is cool! I like the way the video is made!
There also were Pseudo-Static RAM chips (aka Pseudo SRAM, PSRAM) ..
The Sega Genesis (Megadrive) used them, I think.
They behaved like ordinary SRAMs, but were DRAMs with an internal refresher.
Not very fast, but they freed the computer system from the burden of refreshing and could be used do design circuits that could be upgraded to real SRAM eventually.
https://de.wikipedia.org/wiki/Pseudostatisches_RAM
The PSRAM featured on that wiki from 1996 isn’t even that slow – 25-40ns access times is plenty fast for my uses and better than the HM62256-10ALP I use. At least for read times.
I recently bought an rca 1802 cpu im looking forward to putting it on a board and writing an assembler for it. I already have an intel 8085 board.