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Thread: Compact Flash with true 8-bit XT IDE Interface

  1. #1
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    Default Compact Flash with true 8-bit XT IDE Interface

    You can find the original 8-bit IDE interface in a Tandy 1000 TL/2, TL/3, RL, RLX in one form and in the IBM PS/2 Model 25 & 30 (including the 286s for some bizarre reason) in another form. It uses I/O 320-327. From another site, http://www.electronicspoint.com/comp...de-t66828.html, I read this :

    The CF spec requires that all compliant cards support 8-bit transfers in True-IDE mode. In the ATA-2 spec, you simply use the Set Features command (0xEF), and use feature 0x01, which is "Enable 8-bit data transfer". ATA-3 and up seems to have removed it entirely.

    So it seems like CF cards should work in these machines, right? Of course, this assumes that the CF card retains that setting when the power is off or it is removed from an IDE adapter. Additionally, XT IDE drives seemingly only came in 20 and 40MB varieties, while CF cards come in 16, 32 & 64MB versions.
    Last edited by Great Hierophant; September 27th, 2012 at 02:46 PM.
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    The old XTA "8 bit IDE" interface is very different from that of the ATA "16 bit IDE" one. Different ports, bits in the ports, etc.--XTA pretty much conforms to the conventions of the original 5160 MFM controller, while the CF card is strictly ATA--conforming in general to the 5170 MFM controller. Yes, there's an 8-bit transfer mode (and James uses it on his XTCFV2 card), but the registers and port conventions stay ATA.

  3. #3

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    Quote Originally Posted by Great Hierophant View Post
    You can find the original 8-bit IDE interface in a Tandy 1000 TL/2, TL/3, RL, RLX in one form and in the IBM PS/2 Model 25 & 30 (including the 286s for some bizarre reason) in another form. It uses I/O 320-327.
    The IBM PS/1 model 2011 also uses the same HDD interface. I know it is a 8 bit interface but I couldn't find any info. Are you sure it is 8-bit IDE? I tried to decode some data with the Openbench Logic Sniffer some time ago with no results...

  4. #4

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    Quote Originally Posted by Great Hierophant View Post
    ...this assumes that the CF card retains that setting when the power is off or it is removed from an IDE adapter...
    Unfortunately in true-IDE mode the cards always power-up in 16-bit IO mode (so a set-features command is required before gathering device ID).

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    Quote Originally Posted by nestor View Post
    The IBM PS/1 model 2011 also uses the same HDD interface. I know it is a 8 bit interface but I couldn't find any info. Are you sure it is 8-bit IDE? I tried to decode some data with the Openbench Logic Sniffer some time ago with no results...
    Interestingly, I have a scan of the IBM PS/2 Model 25's Technical Reference and the information about the hard drive interface is extremely sketchy. Scott Mueller identifies these systems as possessing the XT Attachment Interface, a.k.a. XTA, and the pinouts given do match up with what an XTA interface could or should provide. The 44-pin interface provides power as well.

    Chuck(G) says that the interface is essentially the IBM Fixed Disk Adapter, although it seems to use 8 ports, while the IBM card only uses 4. Are there more registers in XTA?

    In order to use a CF card, which has ATA registers with an interface that provides XTA registers, you need some kind of translating hardware in between the interface and drive. Or perhaps a BIOS extension would work, using 320-32F as an alias for 1F0-1F7 and sending the appropriate commands on bootup to put the CF card into 8-bit mode. This would require overriding the built-in BIOS functions, if that is possible.
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

  6. #6

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    The main issue is that ATA uses 3 address lines, vs 2 for XTA. So the problem is how to control that 3rd line. And as stated a BIOS would be needed - so really, a PCB to provide the electrical connections for the CF card and somewhere to store the BIOS.

    Come to think of it, something does come to mind....

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    Quote Originally Posted by pearce_jj View Post
    The main issue is that ATA uses 3 address lines, vs 2 for XTA. So the problem is how to control that 3rd line. And as stated a BIOS would be needed - so really, a PCB to provide the electrical connections for the CF card and somewhere to store the BIOS.

    Come to think of it, something does come to mind....
    IBM's implementation uses A2 in addition to A0 and A1. In the pure implementation, used in the Tandys, A2 is not used. So you would need to wire A2 to pin 36 on the header. There are harder hacks. However, can a BIOS extension override the pre-existing Int 13 functions? As far a BIOS storage, an Ethernet card comes to mind.
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    If the native BIOS adheres to the IBM PCs method of instantiating extension BIOS support, any extension can override the native INT 13n routines. After all, INT 13 is just a vector in low RAM.

    So why not use James' XT-CFV2 card?

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    To avoid using a slot, but since you are going to need a BIOS extension anyway, you must take up a slot since none of these machines have one spare socket, nevermind two (all these systems are 16-bit and need two ROMs).
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  10. #10

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    An easier and cheaper solution:

    http://cgi.ebay.com/170899233210

    Yes, a CF card would use less power and take up less space, but as long as ST-351A/X drives remain readily and inexpensively available, they are the most practical solution for anyone needing an IDE-XT-compatible drive, at least for a desktop machine -- there were some laptops which used 2.5-inch IDE-XT drives, in which case finding a replacement is far more difficult.

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