Image Map Image Map
Page 1 of 3 123 LastLast
Results 1 to 10 of 26

Thread: M24-IDE: a 16-bit IDE adapter for the Olivetti M24 / AT&T 6300

  1. #1
    Join Date
    Aug 2017
    Location
    New York, Rome, London
    Posts
    131

    Lightbulb M24-IDE: a 16-bit IDE adapter for the Olivetti M24 / AT&T 6300

    Hello again -

    As I mentioned my newly-acquired AT&T 6300 is missing a hard drive. I have glitchworks's XT-IDE in my Italian Olivetti M24 and it works flawlessly, so I could just get another one. But I've always wondered if it would be possible to remove the latches and have the IDE device communicate with the M24 through a full 16bit-wide data path? After all that's what an 8086 distinguishes itself for!

    So I have spent a bit of time looking at the bus converter schematics (*) and the sequence of signals on the proprietary Olivetti 16-bit bus connector, and I can see no obvious reason why it should not work.

    Olivetti 16-bit data transfers seem to work very similarly to their ISA counterparts, ie an address is presented on the bus, and if the card asserts a specific line (/IOCS16 in ISA, /16BCH in Olivetti) then a 16-bit transfer takes place. There are differences - in the Olivetti case, during a 16-bit transfer cycle the ISA-compatible command lines (/IOR, /IOW, /MEMR, /MEMW) are disabled and alternative Olivetti lines on the 16-bit connector are used (/XIOR, /XIOW, etc).

    With this knowledge, I sketched a possible, simple interface, essentially a simplification of glitch's design split into two boards: a main one that plugs into the ISA-compatible 8-bit slot, and a smaller one that plugs into the Olivetti 16-bit slot. The two would be connected via a short 12-pin ribbon cable.

    I have not breadborded or tested this at all - my ISA breadboard card is old and cranky, and with this many connections user error or breadboard malfunction would be virtually guaranteed. Also, at $5 a pop for professionally-fabricated prototype PCBs I'm willing to just have a board made with a reasonable starting design and then just debug that. (**)

    So my question is... does anyone see any glaring flaws with my schematic, or any obvious reason why the whole thing would not work?


    (*) The bus converter schematics in the Theory of Operation manual does not exactly match mine - probably a different revision. I have a hand-corrected version if anyone is interested.

    (**) I have also not finished routing it yet. It's a lot more complicated than I thought or, most likely, I'm not very good at it.

    (***) Sorry for the zipped version - I know it's not smaller than the .pdf, but the forum won't allow me to upload .pdf's larger than 48kb...
    Attached Files Attached Files

  2. #2
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    34,369
    Blog Entries
    18

    Default

    Weren't there a couple of revisions of the 6300/M24 bus converter board?

  3. #3
    Join Date
    Jan 2014
    Location
    Melbourne, Australia
    Posts
    558

    Default

    Interesting! What kind of performance could we expect on something like this?
    Bobby.

  4. #4
    Join Date
    Aug 2017
    Location
    New York, Rome, London
    Posts
    131

    Default

    Quote Originally Posted by Chuck(G) View Post
    Weren't there a couple of revisions of the 6300/M24 bus converter board?
    I'm sure there must have been - see examples for sale now on eBay with two, three, or four 16-bit slots... !

  5. #5
    Join Date
    Aug 2017
    Location
    New York, Rome, London
    Posts
    131

    Default

    Quote Originally Posted by bobba84 View Post
    Interesting! What kind of performance could we expect on something like this?
    I don't know for sure as I have not timed the 16-bit I/O cycle, but it should be faster than only currently available solution for these PCs (XT-IDE in Compatibility Mode), which uses two separate 8-bit cycles for each IDE 16-bit data access. It should also be faster than an XT-IDE in "Chuck Mod" version if that could be made to work on the M24, since a 16-bit cycle split into two fake 8-bit cycles by the bus converter is slower than a true single 16-bit cycle (I did check this).

  6. #6
    Join Date
    Sep 2017
    Location
    Principality of Xeon
    Posts
    1,861
    Blog Entries
    1

    Default

    Was there a 286(ed) version of these? I know they did a 386, or at least am reasonably sure.

    This is along the lines of a project I had in mind for the Tandy 2000 a long time ago, that is amending and ide card to work with the 80186 based expansion bus. It uses a 96 pin eurocard connector. It's possible much of that which is needed is already there. The NEC APC III (or PC-9801) has C-Bus, and likewise you could at least expect 16 data lines to be present.

  7. #7
    Join Date
    Mar 2011
    Location
    Atlanta, GA, USA
    Posts
    1,593

    Default

    Quote Originally Posted by 2icebitn View Post
    This is along the lines of a project I had in mind for the Tandy 2000 a long time ago, that is amending and ide card to work with the 80186 based expansion bus.
    Not to hi-jack the thread, but I've looked at doing it for the T2K - and still plan to for Tandy Assembly'19. The T2K - and maybe other work-a-likes - do not have a standard PC BIOS. There is no support for a BIOS option ROM for XT-IDE BIOS. And even if there were, the system ROM in the T2K only has enough of Int 13A to boot-strap DOS from floppy or hard disk and then most of BIOS is replaced from code in IO.SYS - including Int 13A.

    The T2K does use a WD1010/1100 combo on it's hard drive controller - which IDE was based on. And it appears that even though hardware designers added support for DMA and IRQ on sector transfer, the code still only uses PIO and busy-waits. So it may be possible to map an IDE drive's register set in the same spot and things 'just work' - in 8 bit mode. The T2K does use a 80186 - unlike the PC6300's 8086. So the designers heavily leveraged the built-in programmable chip-select lines to make peripheral card decoding easier.

    I'm afraid in order to do a lot more with the T2K, most of the BIOS code needs to be ripped from IO.SYS, combined with the ROM, and updated to a proper PC clone compatible code-base - and placed back in ROM. There is only 16KB of ROM window, but it should be doable - skipping pedantic things like placing handlers at the same segment address as IBM! That's why I disassembled and annotated the T2K ROM and was about half way done with IO.SYS when a squirrel ran by. It would break loading the T2K specific DOS flavors but would allow running of more modern stock DOS versions. I plan on finishing and getting MS-DOS 6.22 booting on it as step 1 toward hard drive emulation.

    -Alan
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

  8. #8
    Join Date
    Aug 2017
    Location
    New York, Rome, London
    Posts
    131

    Default

    Quote Originally Posted by 2icebitn View Post
    Was there a 286(ed) version of these? I know they did a 386, or at least am reasonably sure.
    So I read, but I have not had one personally.

    Quote Originally Posted by 2icebitn View Post
    This is along the lines of a project I had in mind for the Tandy 2000 a long time ago, that is amending and ide card to work with the 80186 based expansion bus. It uses a 96 pin eurocard connector. It's possible much of that which is needed is already there. The NEC APC III (or PC-9801) has C-Bus, and likewise you could at least expect 16 data lines to be present.
    Yes I have often wondered whether and to what extent these pre-IBM-AT 8086-based PCs had 16-bit expansion cards available for them back in the day. The only such 16-bit cards seen with any regularity on eBay are memory expansion boards for the M24... but maybe I missed others the existence of which I am not aware of.

    In your design, did you make use of the IDE (or ISA) /IOCS16 signal? In my design I critically rely on it working as I expect to select between 8-bit and 16-bit IDE register accesses...

  9. #9
    Join Date
    Aug 2017
    Location
    New York, Rome, London
    Posts
    131

    Default

    Just a quick update... I finally finished routing it (yep, a year later!). Here is a render of the main board:

    m24ide.jpg

    and one of the little board that goes into the 16bit slot:

    16bus.jpg

    I did not put any mounting holes to attach a bracket... mostly because I could not figure out where to place them (suggestions welcome).

  10. #10
    Join Date
    Oct 2014
    Location
    near frankfurt/m, germany
    Posts
    1,054

    Default

    Interesting, and it looks so simple. Will it run with the XT-IDE-BIOS?

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •