Universal ITX Backplane

Build a retro ISA or PC / 104 slot-based system on an ITX format board

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This backplane is initially intended to be used with Sergey Kiselev's Micro8088 or xi8088 PC clones, among others system powered by x86 architecture. However, other old systems could also be developed using FPGAs built or adapted to ISA or PC / 104 type slots, plus other accessories based on these.

Open Source Hardware project, Kicad project files provided across on my GitHub account.

Notice: The project is still in the prototype phase, the first version has been tested and has an identified fault, although easily fixable.

The PCB has several I / O connectors common to all projects:

  • VGA + MonochromeVGA integrated
  • 2 x DB9 ports to be used as serial ports or as joysticks

Additionally, each project can also add a Hat I / O board by adding other specific connectors. For example, an old PC based on a PC / 104 slot could add PS / 2 ports, IDE44 2.0mm connector to connect an external HD or CF, etc ... it must be taken into account that internally the Hat I / O board does not have of a lot of space, several holes have been placed to fasten it to the backplane.

It could integrate other FPGA-based systems in PC / 104 format such as the ZX-Uno, or design a specific I / O addon for the MiSTer FPGA with the USB redirected to the Hat I / O board for access from outside, etc. .. The idea of using the PC / 104 slot instead of ISA could allow the complete system to fit in a Mini-ITX case of very low profile, common and with high availability today, these in addition to being very compact:

some of these, based on pico-ITX power supply and VESA compatible, could even be placed discreetly behind a monitor:

In short, depending on each project, one or the other slots may be necessary. For example, there is a vertical VGA connector on the backplane (that bridges the output to the VGA connector of the I / O shield) whose purpose is to be able to connect it to a VGA card connected to an ISA2 or ISA3 connectors, placed these further back than its usual place, so it will be necessary to detach the I/O bracket from it.

At the moment, the only problem found is related to the on / off system. The 2n3904 transistor footprint had the Emitter and Base pins swapped due to a mistake of mine copying it from another design with another transistor... but nothing that can't be fixed easily. Without this fix, the boot button would not work...


Once fixed, the system apparently works perfectly. It remains to connect other cards such as the video one, to verify that everything is in order ... I am waiting to have one:

  • Version 1. 0

    Aitor Gómez García10/12/2020 at 17:35 0 comments

    First version of project

    • 4 Layer Mini-ITX board
    • 3 x ISA 8 / 16 bits slots
    • 1 x PC104 8 / 16 bits slot
    • 3 x ISA 8 bits slots
    • I/O shield with MonochromeVGA integrated, VGA, and 2 x DB9 connectors

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