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Unknown 8086 with unknown problems

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First post, by DBob

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Hi folks!

I've bought a 8086 not so long ago. It's small, it's cute, and it's not working the way i like it 🙁

First of all, here's some picture of it (1,2,3,4,5,6).

I've searched a lot for the jumper guide of the manual, without any luck. The shape of the board is like a full length, full height isa card, and all of the extension cards are connected through a 16 bit isa riser card (but the mobo has only pins at the 8 bit part of the bus).

The first and biggest of all problems, that I want to install a SCSI card. So I did. It's an Adaptec 1542CF, with the "less jumper, more software bios" feature. The mobo mostly doesn't react to it, it's rare when I see the Adaptec's bios message at the post process. When the bios of SCSI card can successfully "interrupt" the post procedure, there is always an error about "bios initialization error" and something about shadow ram (I forgot to write down the exact message). Maybe the card wants to copy the value of the bios rom, to the same address in ram, and it's failing because this area is upper to the 640kB.

So...the mobo has only 640kB dip ram installed and there was 4 empty simm ram place, I've installed ~4mb of ram, but the mobo saw only the on-board 640kB. Changed the ram modules..maybe I've installed them incorrectly, or something else. Nothing changed with different rams. Maybe there's something to do with the jumpers on the board, but without any jumper reference I don't really want to. 😒

That's where I'm stuck...any idea? 😀

Reply 1 of 4, by h-a-l-9000

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Is the 1542CF 8086 compatibe? The 8086 doesn't have all instructions the later processors have.

If at all, you are only going to see ram > 640k as EMS, if the hardware supports it and you have the proper driver. 8086s have only 1MB direct address space.

The Vintage Computer Forum would be a good place to ask.

1+1=10

Reply 2 of 4, by DBob

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Is the 1542CF 8086 compatibe?

Good question. I've got no other isa scsi card with bios to try something else. But first I want the mobo to see the simm ram I've installed.

If at all, you are only going to see ram > 640k as EMS, if the hardware supports it and you have the proper driver. 8086s have only 1MB direct address space.

I don't think any programs would see any of the ram area called umb between 640kB and 1MB. DOS itself maybe can loaded there from a 8086...don't know for sure. The only reason why I want more then 640k ram, is that the "shadow ram error" should disappear...hopefully.

The Vintage Computer Forum would be a good place to ask.

Thanks.

Reply 3 of 4, by h-a-l-9000

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Looks like your CPU card only interfaces 8 bits to the ISA bus (photo 5). The 1542CF is a true 16-bit card and I doubt it can work with 8 bits only. You might have more luck with one of these primitive 8-bit SCSI host adapters.

The OTI-031 system controller (http://www.datasheet4u.com/download.php?id=578793) supports 640k (should be the on-board DRAMS on the right side) + up to 8MB EMS (SIMMS) which are extra hardware memory. No mention of mapping some of it to >640k.

1+1=10

Reply 4 of 4, by DBob

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Unfortunately that's the only card scsi card here. This would be a perfect card, if i could get from somewhere.

Pretty awesome (and useless), that a 8086 can handle 8mb memory by this chipset. But the hole in the memory would be weird. It could be checked with lot of tools if there is really a hole between 640kB and 1MB, (after i've got it working.

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