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From: manson@tut.cis.ohio-state.edu (Bob Manson)
Newsgroups: comp.sys.m68k
Subject: Re: DTACK*
Message-ID: <503@tut.cis.ohio-state.edu>
Date: Sat, 17-Oct-87 01:09:53 EDT
Article-I.D.: tut.503
Posted: Sat Oct 17 01:09:53 1987
Date-Received: Sun, 18-Oct-87 09:38:57 EDT
References: <4215@pyr.gatech.EDU> <1613@bloom-beacon.MIT.EDU>
Organization: The Ohio State University Dept of Computer and Information Science
Lines: 25


In article <4215@pyr.gatech.EDU> jkg@pyr.UUCP (Jim Greenlee) writes:
>I have a basic fundamental (probably stupid) question about DTACK*. I was
>told  (by a Motorola person) that it was possible to wire DTACK* directly
>to ground and have a 68000 system run at full speed, provided the memory
>access time was fast enough. 

DTACK* is not supposed to be low for more than, I think it's 120 NS (I don't
have a data book handy, I'm not sure about the exact time) after AS* goes
high, and the results are not guaranteed to do anything (there are certainly
better ways to make hardware single-steppers, and yes, there are uses for
them). Certainly the behavior may not be the same between different
manufacturers and/or various versions. If you want max speed, tie AS* to
DTACK*. That's as good as you'll get, as it'll run (according to the docs) at
maximum throughput. I'm not sure why you wouldn't want to sync the board with
memory, though-if the RAM is really that fast, how much delay can there be in 
generating an on-board DTACK* ? (Dumb question, I know...)
						Bob Manson
...!cbosgd!cis.ohio-state.edu!manson (I'm not sure about that-our
				     address seems to be variable)
manson@tut.cis.ohio-state.edu 


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