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From: bcase@cup.portal.com (Brian bcase Case)
Newsgroups: comp.arch
Subject: Re: Next computer (Re: CISC Silent Spring)
Message-ID: <26767@cup.portal.com>
Date: 9 Feb 90 21:26:19 GMT
References: <8859@portia.Stanford.EDU> <20056@netnews.upenn.edu>
  <486@taniwha.UUCP> <38464@apple.Apple.COM>
Organization: The Portal System (TM)
Lines: 20

>>Look closely at the architecture (try the Byte article), the NeXT board
>>multiplexes data/addresses from the '030 to make it look like the '040
>>(or NuBus) - this means that their silicon is probably already set up
>>for the '040
>
>Um, I hate to break it to you, but the '040 has separate 32 bit address and
>data busses. They are not mulitplexed. They do not resemble the multiplexed
>address/data of Nubus.

Ah, but there is a mode bit (or is this one of the things that is set
at reset time like on the R2000/R3000...) that allows the 040 address
and data bus to be literally tied together to form a muxed bus.  Still,
I seriously doubt this had anything to do with the system design of the
NeXT.

Also interesting about the 040, the output impedance of the output
drivers on the chip is selectable at either 4 or 30 Ohms (I might
have the numbers slightly wrong).  The idea is that you can have
speed at the cost of terminating properly or you can have simplicity
(no termination) at the cost of speed.