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Thread: 25 pin keyboard?

  1. #1

    Default 25 pin keyboard?

    I may find myself in possession of an "AVL Eagle I" which was a CP/M based, single-purpose computer from about 1978, designed to program multi-image slideshows. I am getting the CPU only. The first challenge for me is to find a keyboard that will work with its 25 pin connector! Any ideas on how to start here? I already have a floppy drive and boot disks, all of which I THINK work..

    Snap 2019-07-02 at 12.45.07.jpg AVL_Eagle_I.jpg

  2. #2

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    At that time, DB-25 connectors were often RS-232 serial (but some vendors "broke" with that convention). If it is a serial port, then you could connect almost anything. Of course, the IBM-PC changed the convention for DB-25 to be a parallel port, but this device predates all that nonsense. You might need to trace it back inside to get an idea of what it is.
    - Doug

  3. #3

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    as Doug said i would open it to see as it maybe just using some pins for TX/RX rts/dts grd etc.. like a serial terminal.

  4. #4

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    I agree with Doug that you need to trace the connector back. I'd have thought it would be a parallel keyboard interface, rather than serial though, but who knows! My LSI M-Three system here has such a 25 pin keyboard connector to exchange parallel data between the keyboard and a general purpose PD8255A programmable input/output device on the motherboard.
    CP/M-86 Software Repository www.eolith.co.uk

  5. #5
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    The DB-25 connector was very heavily used and therefore was available at a good price, and many computer makers had a good supply of them already. So it wasn't terribly uncommon to find them being used for purposes other than RS-232 communication. Commercial designers have the same tendency to use parts they have on-hand as hobbyists do (and sometimes they are encouraged to do so when the company has found itself heavily overstocked on a particular component).

    I think there are three possibilities here: a serial interface (likely RS-232 if so), a parallel character interface (probably ASCII codes), or a direct interface to a row/column keyboard scan matrix. It should be obvious which of these three if you open up the keyboard and trace where the connector pins go. You may also get some hints from seeing where the keyboard pins in the system unit go (e.g. if they go to a 1489 chip it is very likely serial).

  6. #6
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    My guess is that it's a parallel interface. All models of Eagle, from the I to the IV, pretty much kept the same basic internal design. One can see how the keyboard from the original AVL Eagle matches up with the keyboard from an Eagle II.

    There are a couple of Eagle schematics here on bitsavers that may shed some light.

  7. #7

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    Well I have not convinced the owner to sell me the rig yet. So far I have found exactly ONE keyboard that uses a 25 pin connection - it is apparently a parallel connector. https://www.ebay.com/itm//231926527489

    Snap 2019-07-10 at 12.35.20.jpg

  8. #8
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    I believe that's a keyboard used to attach to an early notebook PC's printer port.

  9. #9

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    After several months I finally was able to get an Eagle I CPU. Now I have all the components EXCEPT the keyboard. Another forum member has a keyboard and sent me a bunch of photos of the inside and outside. Can anyone discern from these if this keyboard is a parallel, serial, or uses some unique config? Thanks!

    Eagle keyboard 6_800.jpgEagle Keyboard 1_800.jpgEagle keyboard 2_800.jpgEagle keyboard 3_800.jpgEagle keyboard 4_800.jpgEagle keyboard 5_800.jpg

  10. #10

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    Does that mean you have the little board in the back? The keyboard it self looks to be a parallel keyboard. I don't know what the board in the back does. It doesn't have enough wires to both power the keyboard and do parallel. It must be doing some type of serial. I don't know why it has so many wires though.
    Let me think, +V, -V, ground, data, and data clock. That is only 5 pins.
    There are 9 wires. There looks to be a buffer chip there. What is the part type?
    Dwight

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