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small 68000 SBC

norwestrzh

Experienced Member
Joined
Jan 11, 2021
Messages
97
Location
mount vernon, wa
Here's a small homebrew 68000. It has 2 MB of SRAM and 128k of EEPROM. Runs at 25 MHz. Two serial ports at 38.4k baud via a 68681 DUART. It has a compact flash interface via a Toshiba 82C55A. Currently running CP/M 68k (v1.3) with sixteen 8 MB "disk drives" on the compact flash.
 

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Do you have plans to release the schematics, Gerber files, code, etc?
I suppose that I could do that .... at least the Gerbers. But how? I used to have a "user Web site" on Google where I posted details of a lot of my projects (www.hanscom.us), but several years ago Google "upgraded" the format of their sites and completely destroyed their usefulness for distributing information like that. *frown* There's direct contact information (I believe) in what's left of that Google site. If you drop me an e-mail at that address, I can send you the .zip file that was used to produce the PCB at JLCPCB. I also have no problem releasing the code (firmware and compact flash image), but that will take quite a bit more effort on my part to pull it together, so maybe further on down the road? And again, how would I do that? Much larger files.

I must stress that I'm not able to provide a lot of support for a project like this. I'm just an amateur.

Roger
 
GitHub is probably the most typical place to host projects like this. I’d love to check out the circuit design and potentially build one to mess with. Nice work. It’s a great accomplishment to design something like this from scratch!
 
As a follow-up to my post above, I used the same basic design but with a FreeScale MC68SEC000FU20 CPU. I find soldering TQFP .8mm parts very <ahem> challenging, but my friend is a soldering whiz. He provided me with the CPU on an adapter board (thanks Johan!) that I used as sort of a daughter board on the main PCB. I just got done building the board, and find that it will run both a monitor and CP/M 68K at 32 MHz very nicely!! I find that quite amazing for a simple through hole 2-layer PCB. My friend told me that he was able to "free run" the CPU at 50 MHz. I tried to run the PCB at 40 MHz, and the monitor will run, but it can't boot up CP/M 68k. I suspect it is at the "ragged edge" of the timing of the support circuitry. I'd like to try to run it at 36 or 38, but I don't have any oscillators. I'll have to order some.

WRT the suggestions above that I put this design on GitHub, I'd rather not do that. If anybody wants to experiment with either the PLCC board (above) or the 68SEC000 board, just message me and I'll respond with the zip file used to fab. the board. That way you can use the fab. house of your choice. I used JLCPCB.

Roger
 

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I suppose that I could do that .... at least the Gerbers. But how? I used to have a "user Web site" on Google where I posted details of a lot of my projects (www.hanscom.us), but several years ago Google "upgraded" the format of their sites and completely destroyed their usefulness for distributing information like that. *frown*
I may be a bit old-school here, but to my mind there's nothing better than a big ol' "pile of files" for distributing information about projects like this. Writeups go into text files (in Markdown format in .md files if you're feeling particularly energetic—but note that these are still text files you can read in any editor!), pictures go into .jpg or .png files or whatever, and the rest is whatever it is. Using subdirectories is helpful, but not required.

Put this all in a Git repo and you have an easy way of copying it back and forth, including any changes you make to it as time goes on. Put that repo up on one of the many Git hosting services, (GitHub.com, GitLab.com, GitLab set up on your own server, a zillion other options, and now others can see it and even offer improvements and fixes. You can even just drop a Git repo onto any old HTTP server, run git-update-server-info in it, and now people can git clone from that URL.)
 
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