Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!sco!gorn!filbo
From: filbo@gorn.santa-cruz.ca.us (Bela Lubkin)
Newsgroups: comp.sys.amiga
Subject: Re: Non-Zorro slots in the Amiga 3000
Keywords: 3000 slots
Message-ID: <102.filbo@gorn.santa-cruz.ca.us>
Date: 14 Dec 89 19:17:33 GMT
References: <1935@ntmtka.mn.org> <20643@pasteur.Berkeley.EDU>
Distribution: na
Lines: 58
X-Claimer: I >am< R Pentomino!

What kinds of bus might we expect in there?

Zorro II -- 100-pin -- Amiga 2000 compatible.
Zorro III -- more pins -- Amiga 3000 specific.
IBM PC -- 62 (?) pins -- Amiga 2000 compatible.
IBM AT -- 30 (?) pin extension -- Amiga 2000 compatible.
386/486 -- many "standards" or make one up -- mainly for 32-bit memory.

What would be really nice is if the same form factors could be made to
work for all.  From the Amiga perspective there might be a Zorro II slot
with an extension that makes it into Zorro III.  From the IBM
perspective there might be an AT slot with a 32-bit extension for
386/486 memory.  It would look something like this:

+---------------------------------------------------------------------+
| ----- PC ----- -- AT -- == 32-bit == ========== Zorro II ========== | 1
|
| -------------- -------- ============ ============================== | 2
|
| -------------- -------- ============ ============================== | 3
|
| -------------- -------- ============ ============================== | 4
|
| -------------- -------- ============ ============================== | 5
|                         ~~~~~~~~~~~~
| ============== ======== ============ ============================== | 6
|
| ============== ======== ============ ------------------------------ | 7
|
| ============== ======== ============ ------------------------------ | 8
+---------------------------------------------------------------------+

All "==" and "--" are physical slots.  "==" are active, "--" are
inactive.  "~~" represents electrical isolation between adjacent slots.
In the absense of a bridge board, all slots are 16/32-bit Zorro II/III.
In the presence of a bridge board, slots above the bridge board are
Zorro II/III; the bridge board itself uses the Zorro II part of the bus
to interface with the Amiga side, and activates the other three sections
as an AT bus with 32-bit extension.  This allows all the slots to be
used for Amiga (Zorro II or III) boards; or, with a bridgeboard in the
first slot, allows all the rest to be used for PC boards.  You can
reallocate slots by simply moving the bridgeboard.  In the setup above,
slots 1-5 are allocated for Amiga boards, 6 has the bridgeboard, and 7-8
are available for PC, AT or 32-bit PC boards.

Unfortunately, there's a big detail I'm leaving out.  HOW does the
bridgeboard electrically isolate the Amiga 32-bit extension from the PC
32-bit extension?  I don't know.  I'm sure there's a way.

"A way": I would not buy it if this was how it was done, but as an
example to prove that it's possible, you could put hinges in the 32-bit
extension bus traces between each two slots and design the bridge card
to physically swing open those hinges.  Now, is there a >reasonable< way
to do it?

Bela Lubkin    * *    //  filbo@gorn.santa-cruz.ca.us  CI$: 73047,1112 (slow)
     @       * *     //  belal@sco.com  ..ucbvax!ucscc!{gorn!filbo,sco!belal}
R Pentomino    *   \X/  Filbo @ Pyrzqxgl +408-476-4633 and XBBS +408-476-4945