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  • Writer's picturerehsd

80386 DX Build

Updated: Sep 8, 2023

While I continue to build out my 286 (386 SX) system, I thought I would start learning more about the 80386 DX. I am hoping to have a system board at some point supporting a 32-bit 386 DX. I will share updates to my progress in this post. Check back periodically.

This is the Bus Control Logic diagram I am referencing to get me started:

Since posting the above video, I have rearranged the proto board a bit. I have a fully-routed four-layer PCB, but I am hoping to have a two-layer version. The four-layer PCB priced up at over $80 USD for a set of five... ouch. Also, I anticipate I will need to cut traces and run bodge wires as I better understand the design requirements. Two-layer PCBs are easier to work with from the perspective of cutting traces and running bodge wires.

As part of the updated two-layer design, I have added a pair of GAL16V8's. I am hoping to implement Intel's provide code on these two GALs, allowing me to go without one or two of the PSoCs.

Schematic_386DX Proto1_2023-06-22
Download PDF • 1.27MB

I have received the first version of the proto board. I think the board looks great. It's huge!

As I work through the buildout of this 386DX prototype, I'll use the following visual to indicate where my focus is.

I have found the following timing diagram to be helpful.

To Do

Right now, I am thinking of the following order to work through this build. I expect this will change as I go, and I am not sure entirely how far I will get with this first PCB. Checkmarks indicate step completion.

  1. ✅Get basics of a power connector, decoupling capacitor(s), power LED indicator.

  2. ✅Install DS1232 for startup reset (delayed) and auto reset (e.g., in the event of a drop in voltage).

  3. ✅Install 386DX processor socket and processor.

  4. ✅Install the PSoC for clock and reset. Begin working on the programming of this PSoC. I will need CLK2, CLK, and RES right away.

  5. ✅Apply power, check for magic smoke, and see if signals coming out of processor seem reasonable.

  6. ✅Install PAL1 and PAL2 sockets.

  7. ✅Implement code for PAL1 and PAL2. This will require converting ABEL reference design to CUPL. Program and install PAL1 and PAL2.

  8. ✅Continue programming of the clock / reset PSoC to add A0/A1 and S0#/S1# generators.

  9. ✅Install PSoC for decode.

  10. ✅Begin programming for decode PSoC.

  11. ✅Install latches and transceivers.

  12. ✅Install debug headers on bus.

  13. ✅Connect Arduino Mega to debug headers.

  14. ✅Begin debugging.

  15. ✅Install flash ROM with basic BIOS code to test and debug.

  16. ✅Install static RAM.

  17. ✅Continue debugging.

  18. ✅Single ROM with shadowing.

  19. Install VIA.

  20. Install Arduino Nano for SPI-based debugging (serial to PC).

  21. Install PIC.

  22. Install Arduino Nano for keyboard and mouse.

  23. Install ISA slots.

  24. Add ISA VGA card.

  25. Add ISA IDE interface card with CF card installed.

  26. Boot FreeDOS.

  27. Install math co-processor.

  28. Test, test, test.

  29. Celebrate in amazement that I got this far!!

More to come...


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