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From: spp@zabriskie.berkeley.edu (Steve Pope)
Newsgroups: comp.sys.m68k
Subject: Re: 68000 vs. 68020
Message-ID: <13017@pasteur.Berkeley.EDU>
Date: 24 Apr 91 21:03:51 GMT
References: <12964@pasteur.Berkeley.EDU> <27178@hydra.gatech.EDU>
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Reply-To: spp@zabriskie.berkeley.edu.UUCP (Steve Pope)
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In article <27178@hydra.gatech.EDU> byron@cc.gatech.edu (Byron A Jeff) writes:
#>In article <12964@pasteur.Berkeley.EDU> spp@zabriskie.berkeley.edu.UUCP (Steve Pope) writes:
#>>
#>>Perhaps the obvious is worth stating in this discussion --
#>>not only is the 68000 a lower-cost part then the 68020,
#>>but it has a 16-bit bus vs. the 68020's 32 bit bus, and
#>>a somewhat simpler set of control signals.  Therefore, for a 
#>>low end system, the parts count and parts cost will be 
#>>considerably lower for a 68000 system.
#>
#>I'd have to disagree with on on this point. I've built systems with each
#>of the 68008, 68000,68010,68020 and '020 is much easier to hook up because
#>of the dynamic bus sizing. The parts count is actually less than a 68000 or
#>'010 based system because everything can be done on a single 8 bit bus 
#>(Including EPROM, RAM, and I/O). 
#>

I'm surprised to hear that the dynamic bus sizing applies to
instruction fetches.  Motorola's documentation, so far as I
can tell, specifically talks about dynamic sizing for operand
transfers only (for the 68020).  If the dynamic sizing
also applies to fetches then I agree with the above response.

steve