286 microATX motherboard

As of 2021-05-19, this is a unfinished and untested build of a 286 AT-compatible motherboard, inspired by Sergey Kiselev‘s designs.

During the Covid-19 pandemic, I started to build an “enhanced” clone of one of my old computers, a Hyundai Super-286TR. Here are the original specs:

  • Award 286 Bios, for Chips and Technologies Single-Chip AT (SCAT) chipset
  • F82C710 Super I/O with 1x IDE, 1x FDC, 1x Serial and 1x Parallel
  • AMD 286 12 MHz (have to check if it is 12 or 12.5)
  • 1MB RAM
  • VGA OAK OTI-037C 256KB
  • PC Speaker Audio
  • Drives A: (1.2MB 5 1/4″) and B: (1.44MB 3 1/2″)
  • ~40MB HDD – don’t know the model, I was 5 when it broke. Probably a Connor CP3000 or another with the same geometry (type 33 in the BIOS)
  • 8042 AT Keyboard controller
  • 3x 8-bit and 1x 8-bit ISA slots

For this project, I devised the following upgrades:

  • Use F82C235D SCAT and F82C721A Super I/O chipset variants
    • These were chosen due to availability
    • The SCAT is a new variant, fully compatible and bugfixed/more capable
    • The Super I/O will require slight BIOS modifications, but is mostly compatible
  • Support up to 16MHz 286 processors
  • Support up to 8MB RAM
  • Maybe in a later variant: PS/2 mouse support
  • 4x 16-bit ISA slots (can install 8-bit sockets for compatibility with weird peripherals)
  • Adequate termination on the ISA bus and RAM bus to support the increased speed
  • Port 80h debug codes

I sourced various 286 and 386 clones to start the schematics and stopped during the tracing of my original computer motherboard for verification. The main problem was that the chip shortage also influenced retro-hobbyist designs, so I just gave up for the time being. I intend to get back to this, finish tracing and routing to build a test board.

Here are the latest schematics:

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