From: lkoop@TIGGER.STCLOUD.MSUS.EDU (LaMonte Koop)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Zorro III cards?
Date: 1 Sep 92 20:17:43 GMT
Reply-To: lkoop@TIGGER.STCLOUD.MSUS.EDU
Organization: St. Cloud State University, St. Cloud, MN

In article <1992Sep1.182122.9807@maccs.dcss.mcmaster.ca>, rickan@maccs.dcss.mcmaster.ca (Mark Rickan) writes:
>In article <BttoAt.6Cy@gpu.utcs.utoronto.ca> engb@gpu.utcs.utoronto.ca (Ben Eng) writes:
>
>>>Unfortunately, I'm quite certain that the Rambrandt is Zorro II, as PP&S
>>>indicated its A2000/2500 compatibility in the AW Graphics Issue.
>
>>A2000/2500 "compatibility" should not be read as "the card is strictly
>>Zorro II---it does not take advantage of Zorro III features".  It is
>>possible, as I'm sure Dave will explain better than I, to build a card
>>that will operate in Zorro II mode in an A2000/2500 and as a Zorro III
>>card in the A3000 and higher.
>
>Even if this was remotely possible, it certainly wouldn't be feasible.
>In order to take advantage of the Zorro III architecture, you would likely
>have to develop a "double-edged" card, much like the ATI ISA/MCA graphics
>boards. The fact that DMI restricted their Vivid 24 to Zorro III makes it
>rather obvious that real-time 24-bit graphics support is not worthy of
>consideration under Zorro II. It is my understanding that the Rambrandt
>card, while based on the TI34020, is primarily a frame buffer. In the
>end, A2000/2500 compatibility can be read as: don't expect any added
>capability if you have an A3000.

    While this is most probably true for the Rembrandt card specifically,
it is more than 'remotely possible' to design a card to configure itself as
either Zorro-II or Zorro-III, dependant on the bus it resides on.  Unlike
EISA and MCA, Zorro-III is an extention to the Zorro-II spec that does not
utilize a different physical signal arrangement as such. (eg, a new layout).
Rather, Zorro-III is connector-wise physically the same as a Zorro-II 
backplane, which relies not on set signal redefinitions, but rather signal
definitions based upon bus operating modes.
    A Zorro-III capable backplane will operate in one of two modes, which
is dependent on the type of address space being accessed.  For Zorro-II
space accesses, the bus will operate in a Zorro-II compatible manner, allowing
the use of existing Zorro-II cards.  If an access is within Zorro-III defined
space (eg, a full Zorro-III spec card is being accessed), the bus mode will
be that of full Zorro-III bus style accesses, which entail the full new
benefits of that new spec.
    Now, because of the way Zorro-III is designed, it is quite possible indeed
to design a board to either respond as Zorro-II or Zorro-III depending on its
environment.  This would require a bit more work...the card would need to 
configure itself based upon sensing the bus in operation, but it is not at
all far fetched to do this.  The main factor here is the added logic needed
on the board to handle two bus protocols and signal modes.

                 ----------------------------------------
           LaMonte Koop -- SCSU Electrical/Computer Engineering
 Internet: lkoop@tigger.stcloud.msus.edu -OR- f00012@kanga.stcloud.msus.edu
              "You mean you want MORE lights on this thing???"
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Newsgroups: comp.sys.amiga.advocacy