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pearce_jj
July 16th, 2012, 05:05 AM
I'm wondering if the proper IBM card will work in Slot 8 in an XT? And, if it does, whether any boards that use DMA can be used in the expansion unit (for example, a Xebec HDD controller)?

Many thanks.

per
July 16th, 2012, 11:47 AM
I doubt it. I haven't tested myself, but the extender card does not contain any logic to deploy the /cardselect line, so you won't be able to read from any of the ports on the extender/receiver cards themself.

However, the "reserved" signal at the same pin as /cardselect is forwarded by the cable. What this means is that if the extender card is installed in slot 8, all the slots in the expansion unit will act like slot 8. Therefore you can still comunicate with any slot-8-compatible cards installed in the expansion unit.

bettablue
July 16th, 2012, 12:09 PM
I'm wondering if the proper IBM card will work in Slot 8 in an XT? And, if it does, whether any boards that use DMA can be used in the expansion unit (for example, a Xebec HDD controller)?

Many thanks.

From all of the documentation I have gotten from both here in the forums, and on IBMs own manuals, primarilly the Options and Adapters; both the extender and receiver cards need to be installed into the last slot available in either the 5150, or 6160 computers as well as the expansion unit itself. To be honest though, I haven't tried installing them in other slots because once I installed mine as directed, it worked and I didn't have any need to try it in any of the other slots.

Hope this helps.

pearce_jj
July 16th, 2012, 12:55 PM
Thanks very much. Even if it did control B8, my theory is that no DMA transfers can be done from slot 8 because XD[0..7] are interfaced to D[0..7] via U15, but U15 has a gate driven by AENBRD, itself driven high when HOLDA is asserted by the DMA controller. In other words when the 8257 has control of the bus, D[0..7] must be driven by something in an ISA slot other than 8 (or system RAM via U9).

If that interpretation (of the tech ref logic diagrams) is correct, that does fit observed behaviour as I get NMI (parity error) when I try DMA from slot 8.

But the puzzling thing is... why DRQ/DACK signals are present on slot 8, or why the gate on U15 isn't or'd with CARDSLCTD.

per
July 16th, 2012, 01:44 PM
But the puzzling thing is... why DRQ/DACK signals are present on slot 8, or why the gate on U15 isn't or'd with CARDSLCTD.
Maybe that's what they indirectly reffer to when they claim that cards in slot 8 requires "stricter timing" :roll: ...

Great Hierophant
July 16th, 2012, 02:12 PM
Considering that the Expansion Unit comes with a ST-412 and IBM Fixed Disk Drive Adapter (using a Xebec chipset), and those do use DMA, I think its likely that slot 8 will allow DMA usage if the card will otherwise work in slot 8.


I'm wondering if the proper IBM card will work in Slot 8 in an XT? And, if it does, whether any boards that use DMA can be used in the expansion unit (for example, a Xebec HDD controller)?

Many thanks.

Chuck(G)
July 16th, 2012, 03:14 PM
Take a look at the 5160 techref for the receiver card, sheet 2 of the schematics. I haven't worked it through, but whenever I see a flip-flop on a card that normally just passes signals on, I begin to get interested.

bettablue
July 16th, 2012, 03:59 PM
Sorry, but now you're way over my head. The options and adapters manual and the tech ref manuals will have what you want regarding the expansion unit. So that's all I know about it. Everything else is WAAAYYYY over my head. The others who have replied, Chuck and Great Hierophant definitely know what their talking about a hell of a lot more than I do. To me if the manual says to do something, I'll just try to do it. As to why, I have no idea.


Thanks very much. Even if it did control B8, my theory is that no DMA transfers can be done from slot 8 because XD[0..7] are interfaced to D[0..7] via U15, but U15 has a gate driven by AENBRD, itself driven high when HOLDA is asserted by the DMA controller. In other words when the 8257 has control of the bus, D[0..7] must be driven by something in an ISA slot other than 8 (or system RAM via U9).

If that interpretation (of the tech ref logic diagrams) is correct, that does fit observed behaviour as I get NMI (parity error) when I try DMA from slot 8.

But the puzzling thing is... why DRQ/DACK signals are present on slot 8, or why the gate on U15 isn't or'd with CARDSLCTD.

bettablue
August 3rd, 2012, 12:06 PM
Huh? That was confusing.

From everything I've read regarding the expznsion unit, the extender and receiver cards SHOULD ALWAyS be installed in the last slot. So in an XT, that would be slot 8, and on the 5150 PC, slot 5. As far as DMA is concerned; that, I have no idea. Check the guide to operations and IBM options and adapters. Other than these two resources which detail the initial installation of the cards and their locations,there isn't any real information. That's already been verified by me and other members of the forums.

I hope that helps in some way.

per
August 3rd, 2012, 02:06 PM
From everything I've read regarding the expznsion unit, the extender and receiver cards SHOULD ALWAyS be installed in the last slot. So in an XT, that would be slot 8, and on the 5150 PC, slot 5.

Please double-check your sources. I have not seen anywhere in any IBM documents that the expansion card should be placed in slot 8 of the XT. A diagram in The first edition of the Technical Reference for the XT rather suggest it to be placed in slot 1, in fact.

Stone
August 3rd, 2012, 02:57 PM
This is from The IBM Personal Computer XT Hardware Reference Library ... Technical Reference. Page 1-77

9867

modem7
August 3rd, 2012, 03:06 PM
This is from The IBM Personal Computer XT Hardware Reference Library ... Technical Reference. Page 1-77
Per is writing of the extender card, not the receiver card.

pearce_jj
August 3rd, 2012, 11:56 PM
Thanks very much for the input. I'm personally convinced that DMA transfers aren't possible from PC/XT slot 8 since U15 is gated by AENBRD (which = /AEN). But if someone with an expansion unit could test the extender card in slot 8 that would of course be very helpful :)

Great Hierophant
August 4th, 2012, 06:53 AM
Thanks very much for the input. I'm personally convinced that DMA transfers aren't possible from PC/XT slot 8 since U15 is gated by AENBRD (which = /AEN). But if someone with an expansion unit could test the extender card in slot 8 that would of course be very helpful :)

If that is true, then why would IBM put its hard disk controller and drives in the Expansion Unit? The controller uses DMA 3 for transfers, doesn't it?

per
August 4th, 2012, 08:11 AM
Per is writing of the extender card, not the receiver card.

That's problably where the missunderstanding derives from. The receiver card may be placed in slot 8 of the Expansion unit (as it's the bus master an all of that), but the extender card should not be placed in slot 8 of the XT.


If that is true, then why would IBM put its hard disk controller and drives in the Expansion Unit? The controller uses DMA 3 for transfers, doesn't it?

DMA transfers to the expansion unit works as long as the extender card is placed in slot 1 to 7 of the XT. It's only slot 8 that can't do DMA, and that's not just limited to just the extender card.

Chuck(G)
August 4th, 2012, 08:23 AM
All of this asks "Why the special treatment of Slot 8?" I don't think I've ever heard a convincing explanation. It certainly didn't propagate onto the 286 and later systems.

per
August 4th, 2012, 11:13 AM
All of this asks "Why the special treatment of Slot 8?" I don't think I've ever heard a convincing explanation. It certainly didn't propagate onto the 286 and later systems.

It may problably be due to spesifications. An output cannot drive more than a given number of inputs, so perhaps IBM decided to not have more than 15 inputs on a single bus (the TechRef strongly suggests no more than 2 inputs per ISA card)?

An reason why such a number may have been choosed may have been to keep compability with older non-LS TTL chips on ISA cards. Their inputs puts more load on the outputs than the common LS-type TTL chips, and while a LS buffer may be able to drive 30 or so LS inputs, it may only be able to drive 15 older non-LS inputs.

pearce_jj
August 4th, 2012, 11:41 AM
Supporting that, the DMA controller is on the slot-8 side too.

Chuck(G)
August 4th, 2012, 02:42 PM
An reason why such a number may have been choosed may have been to keep compability with older non-LS TTL chips on ISA cards. Their inputs puts more load on the outputs than the common LS-type TTL chips, and while a LS buffer may be able to drive 30 or so LS inputs, it may only be able to drive 15 older non-LS inputs.

LSTTL came out very early in the 1970s. TI claims initial production in 1971. So by the time the 5150 came out, it was very old hat indeed. I'd be surprised to find any manufacturer still designing with plain 7400 logic in 1979.

wdegroot
August 4th, 2012, 04:49 PM
I recall hearing that the "timing characteristics"
of the slot closest to the power supply were different and it was intended for
use withg an :"asycronous card"
meaning a serial card. I think thgis may apply also to a pc 5 slot board
I do not know if another serial card could be used or if the AT satyle 1 s 1p
card could be used. I recall using AT/386 type io cards in my xt and xt clone. I suspect that this did not apply to xt clone motherboards.
BTW therew was a program to "suck out"
genuine IBM basic from the roms and convert the IBM pc dos Basica to a dislk not disk/.rom basic. I stayed with xt class systems long after newer systems were available.

modem7
August 4th, 2012, 05:12 PM
I recall hearing that the "timing characteristics" of the slot closest to the power supply were different
Yes. Per wrote that in post #5.


and it was intended for use withg an :"asycronous card" meaning a serial card.
The IBM Asynchronous Communications Adapter is a card that is compatibile with slot 8.
There are also other cards that can be used in slot 8.
For more information, see http://www.minuszerodegrees.net/5160/misc/5160_slot_8.htm


I think thgis may apply also to a pc 5 slot board
It doesn't.

Chuck(G)
August 4th, 2012, 07:17 PM
Thinking about it, in spite of the number of third-party cards that support Slot 8, and the optional support by the Async card and the Voice Communications Adapter, the funny Slot 8 wiring must have been intended way ahead of time during the 5160 design phase for some special purpose.

There are only two suspects that I can think of--the 5271 (PC 3270) and the PC XT370. Can anyone take a quick look at their library and see if either requires a card in slot 8?