A2091RN hack

[RetroNinja]

Hello, I'm hacking on an A2091. I'm trying to get the XT 8-bit interface to read an XT drive. The SCSI side is working fine. Yes, a SCSI2SD gives me everything I need. This is just hacking. More of the journey vs the destination.

Work Done

• ROM is 6.6 - I've read that XT driver/support info was removed in v7
• 2MB RAM installed
• XT 40 pin header installed
• XT LED header installed
• WD33C93A-PL upgraded to v09
• 74ALS245AN replaced the 74LS245 - I've read this can help Zorro interface
• recapped
• A2091 rev 4 card

ToDo

• add the 14MHz hardware mod - yes, you can add a control/config file for this, I just prefer the hw mod

I'm currently stalled on getting the XT drive to read. The XT interface is limited to 32MB. My current test has been with a PQI DOM 32MB drive. The drive does work fine on my 486SX. Some basics I'm not clear on

• does the scsi.device include control information for the IDE?
• is there a 'best' KS ROM to use
• I have tried the the IDEfix97 ide.device
• when using HDToolbox, what should the DEVICE= ?

 

[jamonyorke]

I've never tried this, but I believe the key is to use a true XT drive, or a dual XT/AT drive such as the ST351A/X (properly jumpered to work on XT mode).

I'd try to find a mechanical HDD like the ones compatible with the Commodore PC10-III / PC20-III

Some examples here:

https://www.zimmers.net/anonftp/pub/cbm-pc/documents/PC-8088-Information.txt

And there it states
"short-lived 8 bit variant of IDE known as XT or XTA. Only a small number of hard drives were manufactured which supported this standard. If a drive does not explicitly state XT compatibility, then it most likely will not work."

 

[RetroNinja]

Thanks for the lead. Others (stachu100 + fitzsteve) suggested an IDE2CF adapter with a super small capacity CF (16MB-ish). Their belief is similar to yours in that they think it may be more compatible than a DOM.

For those interested, I believe this is the pertinent part...

===================

The PC10-III/PC20-III/Colt is extremely limited in what hard drives it can support. As its ISA bus is only 8 bit, it cannot support a full 16 bit IDE interface. Instead it uses a short-lived 8 bit variant of IDE known as XT or XTA. Only a small number of hard drives were manufactured which supported this standard. If a drive does not explicitly state XT compatibility, then it most likely will not work.

Further, the first BIOS revision (4.35) appears to be limited to drives under 20MB. If you use a drive larger than 20MB on an early BIOS, the system will see it as a 10MB drive. With the ST-351A/X, it is possible to set a jumper on the drive to force it into 20MB mode. While this has the unfortunate effect of cutting the drive's capacity in half, it's better than leaving it at the default settings and only getting 10MB. BIOS version 4.36 and above are able to see the ST-351A/X's full size.

XTA compatible hard drives include:
Western Digital 93024, 93028, 93034, 93044, 93048 (20-40MB) (95xxx variants are the same as the 93xxxs, but mounted in 5.25" adapters) - VERY UNRELIABLE
Conner CP-2024XT (21MB)
Seagate ST-351A/X (43MB) (Can be jumpered for either AT or XT mode)
Seagate ST-325X (21MB)
Miniscribe 8450XT (42MB)

Of these models, the ST-325X and ST-351A/X are probably the best choices. The ST-325X is ideal for machines with early BIOS chips. The ST-351A/X can give greater capacity in later systems, or be jumpered to 20mb for early machines. They are both quiet running and reliable. The Western Digital models should be avoided, despite being used in the 20-III from the factory, as they are highly unreliable.


===================

 

[Fastdruid]

DMAC itself generates an 8-bit PC XT(A) interface. This communicates with the WD33C93 for actual SCSI.

The WD33C93A-PL and 14Mhz mod are pointless if you're trying to read an XT(A) drive. They're only applicable to SCSI drives.

My suspicion on the basis of googling what a "PQI DOM 32MB drive" is that you're actually trying an ATA drive (16 bit) not an XTA (8 bit) drive.

https://acceed.com/media/manual/manuals/pqi-dom-019.pdf

If that is the case then it will never work.

 

[RetroNinja]

DMAC itself generates an 8-bit PC XT(A) interface. This communicates with the WD33C93 for actual SCSI.

The WD33C93A-PL and 14Mhz mod are pointless if you're trying to read an XT(A) drive. They're only applicable to SCSI drives.

My suspicion on the basis of googling what a "PQI DOM 32MB drive" is that you're actually trying an ATA drive (16 bit) not an XTA (8 bit) drive.

https://acceed.com/media/manual/manuals/pqi-dom-019.pdf

If that is the case then it will never work.

Yes, the 14MHz, WD33C93A-PL, recap, and 74ALS245 were more of a 'let's upgrade everything' versus something dedicated to the XT side.

Thanks for catching the ATA vs XTA point. I was too quick to order the DOM and took for granted that the minuscule 32MB size would equal an old XT interface/control. The details matter