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To: riscy@pyramid.com
Subject: Re: EISA?
From: Dan Fishman <dfishman@csn.org>
Date: Wed, 11 Aug 1993 06:36:36 -0600 (MDT)
In-reply-to: <9308111215.AA22768@resi.waldorf-gmbh.de> from "Andreas Busse" at Aug 11, 93 02:15:43 pm
Reply-to: riscy@pyramid.com
Sender: owner-riscy@pyramid.com
> > EISA is a pretty good bus, something like 6 times the bandwidth of ISA.
> Agreed.
> > Isn't it completely upward compatible from ISA (i.e. we can use it just
> > like a ISA bus).
> No, it's completely incompatibel, from all 3 points of view:
> - connector (different pin spacing)
> - hardware  (different signals)
> - software  (probably, don't really know)

You need to tell that to my motherboard.  ISA boards run just fine in EISA
slot connectors (I know, I do it).  The pin spacing is different  in the sense
that there are double the number of pins and they are spaced vertically one 
above another.  I don't know all the tech details, but ISA boards simply make
contact with only their required signals and do not interfere with the added
bus signals for EISA control.

> > I certainly wouldn't object to an EISA bus on the riscy board, and if
> > the ARC chips support it it's practically free.
> No, it wouldn't be free. The ARCset just has a few lines intended
> to be used to control the Intel EISA chipset.
> Again, quoted from the data sheets (uPD31432, page 107):
> The uPD31432 supports two types of external bus masters: 386-type bus
> masters, and an EISA expansion bus interface based on the Intel 82350
> EISA chipset.
> [end of quoted material]
> That means that we can
> a) use the EISA bus (with all the advantages and disadvantages it has)
> b) skip the EISA bus and make our own ISA interface
> c) have no expansion bus at all.
> Ok, we already had a discussion wether we want an expansion bus
> or not and we decided to go with ISA.
> Assuming we have all the really necessary stuff on-board, I would
> go with EISA too. It would make the design faster again and it
> offers more speed.
> On the other hand, not one of the ISA cards people have would
> be useful.

WRONG AGAIN.  ALL ISA boards should work just fine in an EISA bus system.
Again I'm doing just that (though obviously I have'nt used EVERY ISA board).
For example, in my EISA bus I currently have EISA AHA1742, ISA Hercules
Graphics Station video, and I had a DEC ISA Ethernet Card (I forget the 
model) and a SONY CDU535 8-bit ISA bus interface  CDROM drive.  They
all worked just fine and cooperated without a hitch.

> ....... Specific design proposal omitted
> Andy

Dan Fishman (dfishman@csn.org) (W) (303) 469-6469 (Fax) (303) 465-4396

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