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Thread: 8-bits IDE interface

  1. #1

    Default 8-bits IDE interface

    Hallo allemaal,

    Some 8088 PCs, like the Commodore PC20-III and Philips NMS9100, came with the 8-bits IDE interface. Again my thoughts were about using that bus in combination with a CF card and using the XTIDE software to make use it. But again I run into a small challenge: I cannot find any info about this interface? I have the official specs about the official 16-bits SATA interface but haven't found anything about the 8-bits.

    Any info?

    Thank you!
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  2. #2
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    An XT-Bus to IDE (AT-Bus/CF) converter would be a grat thing, I also would love to have one as I have several PCs from Olivetti which have the XT-Bus-interface. I still have working harddisks in these machines, but a replacement would be nice. To be on the safe side, it should be possible the adapter has a kind of setup, where I can set the geometry (cyl, head, sectors) of the emulated harddisk as these PCs are very inflexible (fixed hdd geometry in BIOS).

    Maybe that XT-Bus is very similar to AT-Bus, same command set, but only different signals (8 instead of 16 data bits), I remember a drive from Conner which could be used on both interfaces.

  3. #3
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    An old discussion of the XT IDE pinout can be found http://www.vcfed.org/forum/archive/i...p/t-39749.html Note that the AT IDE uses the pins alecv labels as A2-A9 to transfer the other 8-bits of a 16-bit transfer Some other pins in use on AT IDE are ground pins on XT IDE. It isn't an easy thing to get AT IDE drives to work on XT IDE adapters without altering the firmware on the drive.

    I know I found a much better reference several years ago but I can't locate it. May do a follow up if I remember where.

  4. #4
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    Normally, the "8 bit IDE" interface is known as XTA, in contrast to the "16 bit IDE" interface or ATA. Although the two use the same cable, the internal organization of the XTA interface more closely resembles that of the PC XT ST506 controller (i.e., the register definitions are different).

    This is not to be confused with the "8 bit data transfer" option defined in the ATA standard. Using command EFh, sending 01h enables 8 bit transfer mode (if supported); 81h disables it. I have yet to find an IDE drive that supports this mode--perhaps it was implemented on an early model. However, 8 bit transfers are implemented on CF cards. That makes sense, if you recall that most CF cards are used in portable devices with low-power microcontrollers. Dedicating 16 lines to data transfer might incur extra design costs.

    The best place to find information on XTA is to look up the reference material for a given XTA drive. There really never was, as far as I'm aware, an official standard for it--it was more of a de facto vendor's convention.

  5. #5

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    Thank you all for answering!

    I never saw the abbreviation XTA before so I learned something again. About the registers, I tried to disassemble the HDD part of the BIOS of a PC20-III and then I already noticed the difference with the register of an ATA drive. IIRC I even noticed the BIOS only used three registers, anyway certainly not the eight used by ATA. Not knowing at all what these registers did, further disassembling was undoable (or better: not worth all the needed time).

    As said in my first message, an idea was to see if it is possible to connect a CF card. But looking at the pinout given by Krebizfan I noticed there are only two address lines and we need three. (There is also one CS line missing but we don't really need it) Bummer
    Hmmm, what is this PRICS pin?

    Now the funny thing: after writing the above I searched for XTA hard drive on google and found this: http://www.vcfed.org/forum/showthrea...sk-Replacement, the link you were looking for?
    I went quickly through the thread and if I understood things correctly, he managed to get an 8-bits range by concatenating two 4-bits ones. Something not possible on my NMS9100 ot PC20-III w/o hardware changes.

    A remark about attaching an HDD instead of a CF somewhere in the thread: it is possible. I use 16-bits IDE HDDs as 8-bits drives for my Commodore 64 by not using the upper eight data bits. Works fine. OK, I can only use half of its capacity but being able to use "only" 10 GB of a 20 GB HDD is not bad for a C64 The only command that won't work is the info command. The information is given as 16-bits and I cannot read that. So I determine the capacity of an HDD by try-and-error using a smart algorithm.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  6. #6
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    eeguru's NetPi-IDE is probably going to end up being the best long-term solution for systems with XTA drives. IIRC, he's said that it should be possible to do an XTA implementation on the NetPi-IDE.

  7. #7
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    I'm trying.. I need to get my Jr back out next week and test the ice40 boards.
    "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

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    20190924_110101.jpg

    found this guy in my stash the other day, IIRC it was bundled with an IDE CDROM (that functioned normally when connected to a standard ATA interface)

  9. #9
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    That looks like a more typical "XT-IDE" style controller, nothing to do with XTA drives unfortunately!

  10. #10
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    Quote Originally Posted by maxtherabbit View Post
    20190924_110101.jpg
    found this guy in my stash the other day, IIRC it was bundled with an IDE CDROM (that functioned normally when connected to a standard ATA interface)
    Beware, and make certain that is not a Panasonic/Mitsumi interface card. I have a few of them.

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