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Thread: Tei computer

  1. #1

    Question TEI 8085 S100 computer, no fdc no software...

    Today I've picked up an old TEI S100 system. It has a 8085 CPU. The previous owner used
    it for a decade as an external floppy drive on an IBM compatible machine... How low can you go.
    Well it probably saved the machine it's live...

    The machine has a very, very nice construction. A pleasure to look at.
    Unfortunately the floppy controller is missing. There are only a CPU , I/O and memory board.

    The drives are MPI B52 models. DSDD, that is why they could work on an IBM compatible...
    I found out that Tei had an FDC-2 and FDC-3 floppy controller card. The FDC-2 has
    an 1771 and the FDC-3 an 1791. I would expect that the machine had an FDC-3 controller
    because only this controller could use the full capacity of the floppy drives...

    But FDC-2 or FDC-3, it doesn't matter. I can't find any software for this machine.
    Does anyone have software images for these Tei machines?

    01.jpg 02.jpg 03.jpg
    09.jpg 08.jpg 04.jpg 05.jpg 06.jpg 07.jpg
    10 Tei CPU-85.jpg 11 Tei CPU-85.jpg 12 Tei 64K RAM -4.jpg 13 Tei 64K RAM -4.jpg 14 Tei I-O -2.jpg 15 Tei I-O -2.jpg

    This is a bit special... A constant voltage transformer in this computer...
    You can see the AC capacitor at the arrow.
    16 constant voltage power supply.jpg

    Thanks in advance!

    Regards, Roland
    Last edited by Roland Huisman; April 28th, 2017 at 01:08 AM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  2. #2
    Join Date
    Jan 2010
    Central VA


    Nice find! As you've noted, TEI did make some really well built boxes, I've got one of their smaller units...10 slots I think? CVT like yours, but the CVT in mine is *very* loud, almost like there's a loose lamination or something. I've got an 8080 CPU and 16K of TEI static RAM in mine, those are the only TEI boards I currently own.

    I've avoided buying a TEI floppy controller for the same reason you've encountered -- no software, no documentation! There are many examples of customizing CP/M for 1771 or 1791 FDCs of course. I'm currently using a North Star MDC-A4 single-density hard sectored controller in my TEI chassis, when I use floppies with it.

  3. #3


    Thanks for your reply! This is your cpu card?

    Interesting to see that jump address. I guess you can jump to the
    start address of a floppy controller or an address on an eprom board?

    There is a dipswitch on my cpu board, and an 2716 eprom.
    I don't think the dipswitch is for a jump startaddress. But maybe there
    are a few preset jump addresses in ROM selected by the dipswitches?

    I want to read the rom to check what's in it. My programmer
    can read only 2732 and bigger. So I have to make a little converter.

    Regards, Roland
    Last edited by Roland Huisman; April 28th, 2017 at 12:45 PM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  4. #4
    Join Date
    Jan 2010
    Central VA


    Yes, that's my CPU board! The jump address lets you jump into whatever code you like, a monitor EPROM or a bit of boot code, et c.

    Your board probably just jumps into the EPROM on power-up and/or reset -- many S-100 boards simply turned off the bus drivers and caused the first few reads to come from the EPROM, regardless of what was in the system. In that case, the first three bytes of the EPROM are usually a jump into the proper EPROM address. Some boards implemented it as a hardware jump (like my board) but it was tied to the address selected for the EPROM. The boards may or may not support /PHANTOM for the EPROM. I've seen other arrangements where writing to the EPROM address range would actually write to memory, so the EPROM could copy itself into RAM and then switch off.

  5. #5


    Here you can find the content of the eprom on the cpu board: tei

    In a text editor you can see these text strings:
    "Stock Control International micro DOLPHIN"
    "Met welke drive wilt U beginnen ?" (Dutch for: with which drive do you want to start?)
    "MEER DAN 10 RETRIES !" (Dutch for: more than 10 retries !)

    So the eprom is modified by "Stock Control International" which once sold this computer.
    You can also find "Stock Control International" on the black label on the back of the machine.

    To display these start up texts, the eprom must also contain information about the serial card.
    And besides that, the start address of the original fdc must be in it too...

    I wonder if there is a debugger in it. There is quite a lot of code in it...
    Maybe someone recognises the code?

    Does anyone know a good 8080 disassembler for Windows?

    Regards, Roland
    Last edited by Roland Huisman; April 29th, 2017 at 02:32 PM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  6. #6


    For a disassembler, try DASMx. It does very good multi-pass disassembly and it lets you input your own symbol table to define labels or regions. I used it for a monitor ROM. The best part is that you can run it once and then use that output to define symbols before running it again. By doing a few iterations, you can build up a better assembly source as you figure out the code.

  7. #7


    Thanks, I will try the DASMx. I'm really curious what to find....
    WTB: Case for Altair 8800 ...... Rolands Github projects

  8. #8


    I've been looking at the cpu board for a while. And figured out that the
    8 dip switches are for address setting. Funny how a few addresses were swapped.
    The read out is done by two DM74L85s.

    The switches in the on state give a zero. The address seems to be set at F0xx
    I wonder, what would this address be? The floppy start address? Or the EPROM address? Or...?

    S1 = A15 (off = 1)
    S2 = A12 (off = 1)
    S3 = A14 (off = 1)
    S4 = A13 (off = 1)
    S5 = A11 (on = 0)
    S6 = A10 (on = 0)
    S7 = A9 (on = 0)
    S8 = A8 (on = 0)

    10 Tei CPU-85.jpg

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  9. #9


    Hmm a short test... I've put in E800 (Northstar FDD controller start address) with the switches.
    Pulled out the CPU board out of my Northstar Horizon and put in the Tei controller.

    After hitting reset the floppy starts to read. So then I think it is a Jump address...

    I don't see anything appearing on the screen. I guess CP/M crashes because
    this board has a 8085 and not a Z80...

    But why on earth is there an eprom if there is a jump address? The original address
    setting is F0xx. So I wonder if F0xx is the start address of the eprom...
    I think I'm going to burn a jmp E800 in an eprom and see what happens then.

    Sadly no documentation at all about these Tei CPU 85 boards...

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  10. #10
    Join Date
    Jan 2010
    Central VA


    CP/M will run on an 8085, but if you have a version that does use Z80 opcodes, yes, it will crash! North Star DOS will also work with an 8080/8085 unless it has been customized for a system with a Z80.

    The EPROM may be a ROM monitor, to allow doing system maintenance without having to boot a diskette. Many ROM monitors are like this, and also support jumping to a floppy boot routine (looks like yours does that, since you found a string asking which floppy to boot from).


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