Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!mtxinu!taniwha!paul
From: paul@taniwha.UUCP (Paul Campbell)
Newsgroups: comp.arch
Subject: Re: Next computer (Re: CISC Silent Spring)
Message-ID: <491@taniwha.UUCP>
Date: 12 Feb 90 01:17:13 GMT
References: <8859@portia.Stanford.EDU> <20056@netnews.upenn.edu> <486@taniwha.UUCP> <38464@apple.Apple.COM>
Reply-To: paul@taniwha.UUCP (Paul Campbell)
Organization: Taniwha Systems Design, Oakland
Lines: 29

In article <38464@apple.Apple.COM> baum@apple.UUCP (Allen Baum) writes:
>>In article <486@taniwha.UUCP> paul@taniwha.UUCP (Paul Campbell) writes:
>>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
>
>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.

I know they are not physically multiplexed ... but look at the (synchronous)
timings of TS (start) and TA (ack) (compared with the asynchronous ones used
on previous 68K chips) and how much they are like the equivalent NuBus lines.
You can actually put the '040 into a mode where you can physically tie the
address/data lines together (and run them as a multiplexed bus).

I sure there are also other reasons for NeXT using a multiplexed bus (lower
pin counts on their VLSI for example) but I think that the idea of
multiplexing address/data lines on a workstation (something that is rather
counter-intuitive, not something one would usually do deliberately) is really
rather a bright one! and a really good match for the NuBus too (since you
have to do it anyway).

	Paul


-- 
Paul Campbell    UUCP: ..!mtxinu!taniwha!paul     AppleLink: CAMPBELL.P
You know there's something wrong when 100,000 people marching in Moscow
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