Building an OSI 502B CPU Board

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glitch
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Re: Building an OSI 502B CPU Board

Post by glitch »

Thanks for providing the BoM/assembly notes! Dave, think we ought to add this to the Github repository?
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dave
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Re: Building an OSI 502B CPU Board

Post by dave »

glitch wrote: Wed Sep 04, 2019 12:39 pm Thanks for providing the BoM/assembly notes! Dave, think we ought to add this to the Github repository?
Absolutely. Jeff, thanks for sharing your experience building up these boards.
Jeff
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Location: British Columbia, Canada

Re: Building an OSI 502B CPU Board

Post by Jeff »

Hey, it’s fun to share!

Has anybody else built up these boards? I feel like I’m blazing a trail here one that hasn’t been traveled for over 40 years. If not, hopefully many will follow.

It’s fun to uncover the history of these machines, though.

/Jeff
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dave
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Re: Building an OSI 502B CPU Board

Post by dave »

I think you are blazing a trail. Keep it up!

Dave
waltermixxx
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Re: Building an OSI 502B CPU Board

Post by waltermixxx »

glitch wrote: Mon Sep 02, 2019 2:29 pmI'll be there!
Any chance you might be bringing along a backplane, and enough molex connectors for a 502 and 540B. I would Save on shipping? I’ll be at the Cosmac1802 table along with Josh B and Lee H. Or I can come and find you. :0).
Turning into quite an OSI Junkie (HTFDTH?) Superboard II REV B-40K, 9600b, HC-05 Bluetooth, Superboard II Rev D, C4P rebuild- 502, 542c, 540B. :)
dave
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Re: Building an OSI 502B CPU Board

Post by dave »

I've updated the 502 Altium PCB file and the Gerbers (and 3D rendering) to fix the trace I omitted, and the erroneous OSI trace. I also added Jeff's assembly notes in the doc_dir subdirectory.

I think it would not be too destructive to add some jumpers to select inverting or noninverting chip select lines for the BASIC ROMs, as already exists for the monitor ROM, without violating the spirit of the design, so that no traces would need to be cut (other than pre-wired jumper positions) and U17 would not need to be touched. Best to have a jumper for each ROM, so original ROMs could be mixed with 2716's. For example, one may want to replace only BASIC3 with a 2716 to install the garbage collector fix. I will think about it.

For more involved modifications, it would be better to capture the schematic and link it to the PCB file, but if I put in that effort, I'd rather use KiCad, now that it's getting close to usable, so it would be more useful to more people. Not everyone has Altium Designer 19.
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glitch
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Re: Building an OSI 502B CPU Board

Post by glitch »

I'll have bare boards with me, but no parts kits. I had to hit the road for work on Sunday, so what I packed is what I'll have!

TangentDelta has built up a 502B reproduction, but he didn't build the whole thing since he was planning on using one of my GW-OSI-RAM1 boards for both RAM and ROM. It's a pretty minimal "put the 6502 on the bus" build. He's got a thread on it on the forums.

Dave, I've recently done a project where I've re-implemented and extended the Intel SDK-80. I started with a scan from Mile High Test, imported the copper layers as non-mechanical into KiCAD, and used that for all of my component positioning and a lot of the trace routing. I did capture the schematic as well. It's a fair bit of work but I think that's the "right way" to start doing heavier modifications on old board designs. All in all, it was a full weekend of work, plus a few "come back to it later" sanity checks over a few days, before submitting the files.
Check out The Glitch Works
OSI Challenger 3, 510 CPU, 8" floppies, 23 MB hard disk system starting to work!
Parts bin Challenger 3 board set, never had a chassis in its time
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