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Help Trying to run Adaptec SCSI 1542B On 8086 Machine

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First post, by domelectronics

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Hello everyone,

I am desperately trying to get my beloved 8086 NEC-V20 system up and running with a hard disk.

I have been fiddling with this system for quite a while now. I do not know much about it. The motherboard is branded HIL8 - but this does not give any results on Google ect. It appears to be built by a company called Micro Universe..

As far as the setup, I am trying to use my Adaptec 1542B SCSI with a Quantum 1080S SCSI HDD. At first, I thought I was setting something up wrong with jumpers ect ect, however today, I plugged the whole rig into my Dell Precision 610 with ISA slot and was happy to see that everything was working! I was even able to boot to DOS from the SCSI card + HDD from the Dell.

However when swapping the SCSI setup to the 8086... We have no luck!

So I am wondering:

-Will this even work?

Now on the 8086 Machine, I am running just the pictured VGA card, the Adapte SCSI, and occasionally a very old WDC floppy/MFM controller.

Symptoms are:
8086 with WD card - system works and will boot DOS from floppy
8086 with SCSI card, will boot from floppy WITHOUT HDD connected.
8086 with SCSI card, HDD installed - will attempt to seek HDD, lights stay on, timeout with no boot device
8086 with SCSI card, HDD, floppies hooked up - system will init. HDD, seek floppy for 2 seconds, SCSI card LED and HDD LED come on, system will hang for 5 mins. and boot error.

Help needed please! 😀 Is it even possible to run this setup?! The 8086 works great but I would love to have a hard disk setup. You guys are my last hope! Thanks in advance all!!

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Reply 1 of 6, by Disruptor

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It will not run.
The Adaptec 1542B is a busmaster controller.
Both busmaster control lines and DMA lines are on the 16 bit extension of the ISA bus.

Edit:
Busmaster clarification.

Last edited by Disruptor on 2022-12-18, 10:13. Edited 2 times in total.

Reply 2 of 6, by weedeewee

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Disruptor wrote on 2022-12-18, 09:40:
Does the Adaptec 1542 even run in an 8 bit slot? In selected DMA channel 5 it will not run. Try to change DMA channel to 0 first […]
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Does the Adaptec 1542 even run in an 8 bit slot?
In selected DMA channel 5 it will not run.
Try to change DMA channel to 0 first.
In selected IRQ channel 11 it will not run.
Try to change IRQ channel to 9 first. This is IRQ 2 in a XT.

Exactly ! if this doesn't work then OP is SOL.
also maybe set the dma speed to lowest (J5 pin pair 12 & 13 not jumpered)

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Reply 4 of 6, by Anonymous Coward

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Future Domain TMC-850M is the scsi card you want.

Since when are all 16 bit isa cards backward compatible with xt bus? It’s an exception, not a rule.

"Will the highways on the internets become more few?" -Gee Dubya
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Reply 5 of 6, by domelectronics

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Hi guys,

Thank you for the advice! I did try to switch the DMA and IRQs tonight without luck.

Is there any other trick or perhaps a workaround to get this hardware all working together or no dice?

Thanks again,

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