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Trash80toHP_Mini

Three Slot Riser for 6400 - In search of the Mythical Slot C

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OK this is officially out of hand, from the DevNote's description of the PCI Signals::

IDSEL -  Initialization device select; used during configuration

 

It's fine on A1 (bottom slot) showing right up where it's supposed to on the edge card connector.

IDSEL on B1 (top slot) is another story entirely, the dang thing is tied to Address Line 14 on the 6400 riser! 8-o

 

So during bootup/setup, the system uses A14 to figure out how to talk to a card installed in Slot B1? And here I was thinking there weren't all that many "RESERVED" pins remaining to work through in search of the mythical Slot C1. :lol:

 

One might assume this makes some perverted kind of sense, but  .  .  .

 

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IDSEL's are always wired to an address line.  That's how PCI works.  It's weird, but it makes sense.   I just can't remember how at the moment, or I'd wander off into one of my long explanations.  IIRC, it has something to do with holding some command lines a certain way at initialization and then walking the address lines until a slot sees it on their IDSEL line and responds.

 

Anyway, from what I saw in the C600 riser, I think you'll find IDSEL for slot A goes to address 13, slot B to address 14, slot C to address 15, and I bet whichever pin is used for IDSEL in the comm slot goes to add 16.

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THX, that now makes a lot of sense to me in terms of the cascading nature of PCI slot addressing voodoo.

 

I took a quick look at the remaining lines that are cutout between A1 and B1. Notes are at work for later perusal and I don't remember offhand if it's either PRSNT1 or PRSNT2 that appears to be problematic. Slot A1 connects to the proper contact on the edgecard, but on B1 that pin seems to drop off the ends of the earth. Weird stuff.

 

It's currently looking like hijacking Slot E1 might be a more productive avenue of approach than the Slot C1 quest.

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OOPSIE! That comma wasn't helpful at all. ::)

 

wiremess-000.pdf

 

I've got most of it worked out in a convoluted mess of a diagrams, doodles and tables, but now I've narrowed it down to something practical. I can begin prototyping by hacking together a pair of Flex-Cable PCI Risers, adding a jumper block configuration setup. The few CS2 edge connector lines from that beheaded riser will be woven through the web of the modified PCI Slot riser. the setup will allow testing the Slot B1 patch and an attempt to blow ComSlot2 out to full spec PCI Slot E1 in the same connector bolted up to the side panel of the BenchMac 6500.

 

Then/if/when, I can poke around for the missing lines for Slot C1. The info that IDSEL is tied to A15 is a major step of that campaign, THX, trag! Time for more doodling at work.

 

Edited by Trash80toHP_Mini
typos

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FAIL - first stab at converting the ComSlotII to a full PCI Slot didn't work, but I really wasn'texpecting it to work right out of the gate, if ever.

 

Flexible ribbon cable risers came in today for converting Slot A1 to B1 and to poke around looking for C1, but it's a little complicated to jump right into. So I couldn't resist cobbling together a ComSloII riser to jumper the four required signal lines (Green, Orange, Blue, Red) to the header block of the jumper configurable three slot riser. Oh well, we'll see what the next setup yields.

 

@trag  I left the 3.3V Key pins (A12/A13/B12/B13) floating on the first try and grounded them on the second. Didn't figure it mattered because a 3.3V slotted riser works fine as A1. Does it matter after all? Gotta get B1 right for the low profile twin slot adapter. C1's a unicorn hunt.

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