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Homebrew 486 SBC/computer project

Discussion in 'General Electronics Discussion' started by Solidus, Jul 9, 2013.

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  1. Solidus


    Jun 19, 2011
    Originally, I was going to post this in the Datasheets section as that is my principal concern but I decided to post it here so everyone can follow and give their guidance on the project overall as well.

    Right now I am working and researching in computer processor architecture, so I decided to design a 486-class single-board computer project. The processor I plan on using is an Am5x86 133MHz CPU. I've studied the microprocessor-level architecture enough so that I've designed a rudimentary processor that would do some simple tasks, but data handling doesn't explain how the thing does what it does. Building a computer from scratch helps elucidate that some. It helps shine light on how the processor handles the external world.

    I picked the project as it is sufficiently hard (i.e. unlike Z80 builds, there aren't a half-million retro-computing schematics and resources out there, so I'd have to do it all mostly from scratch and learn the hard way. This isn't to put down or dismiss those builds, but I wanted a project where I would be forced to learn about the architecture from the ground up), and yet it is early enough in the x86/IA-32 processor lineage that the complicated bussing and interfacing schemes weren't yet developed to the level of complexity they are now.

    I also decided on it due to the fact that I have an old Texas Instruments 4000e laptop laying around, which I could deconstruct to find the particular chipsets and use datasheets to reference the layouts on.

    Main problem I have is, upon cracking the laptop open, I see the processor and can determine its pinouts fine, but there is a TI chip next to it, marked F169440PPM. I'll be damned if this isn't the most obscure chip out there - I cannot find a datasheet or information on it aside from it being QFP-208 anywhere.

    It can't be a north or southbridge, as those bridging protocols weren't developed yet. It could possibly be a bus controller, although from looking at a lot of the support chips of the time it seems most chips were directly ("CPU Local Bus") interfaced to the data and addressing busses off the microprocessor. I've discounted PCI or ISA bus controllers, as there are no peripheral slots. Finally, it could be a DRAM controller, although I don't see why they would mount the package smack in the middle of the traces.

    Hence why I have turned to y'all electronics gurus to help me with the project. If any of you have other ideas for how I should carry out this project, resources or learning tools or schematics to help me get the architecture down, I will be most grateful. In that case, keep in mind I will be getting a minimum of 3 boards from the PCB fab ;)

    I can supply you with photos of the laptop mobo itself, links to CPU datasheets for both the processor I'm using and what is mounted, and Eagle schematics and board layouts. I will readily share every resource I have at my disposal if anyone can help me get answers with which to continue to carry out this project.
    Last edited: Jul 9, 2013
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