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Path: utzoo!mnetor!seismo!columbia!caip!cbmvax!daveh
From: daveh@cbmvax.cbm.UUCP (Dave Haynie)
Newsgroups: net.micro.68k
Subject: Re: Re: Re: BYTE "68000" issue
Message-ID: <732@cbmvax.cbmvax.cbm.UUCP>
Date: Fri, 12-Sep-86 16:16:00 EDT
Article-I.D.: cbmvax.732
Posted: Fri Sep 12 16:16:00 1986
Date-Received: Fri, 12-Sep-86 22:28:14 EDT
References: <3531@ism780c.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 35

> 
> In article <710@cbmvax.cbmvax.cbm.UUCP> daveh@cbmvax.cbm.UUCP (Dave Haynie) writes:
>> Incidently, as far as I've heard, none of the top 3 popular 68000
>> systems support the TAS instruction.  The AMIGA executes a read
>> cycle for TAS; I believe that it will crash either the Atari ST
>> or Apple MAC.
> 
> Sounds like someone is using AS to de-assert DTACK rather than UDS and
> LDS.  Is this correct?
> 
> In the micro lab class I took when I was a student at Caltech, about half
> the 68k systems students designed had this problem.
> -- 
> I admit it!  I don't believe in Mary Worth!  I Lied!  HaHaHaHaHaHa!!!!!!
> 
> Tim Smith       USENET: sdcrdcf!ism780c!tim   Compuserve: 72257,3706
> 		Delphi or GEnie: mnementh

I'm not sure if they look at /AS or /UDS and /LDS, but that's not the main
reason.  In the Amiga at least, the video processors share half of the
memory cycle time (S0-S3).  There's not enough time on the DRAM bus for a
Read-Modify-Write cycle.  While the ST and MAC system aren't doing things
as complex with their video displays, they do share the bus and probably
have similar memory constraints.

-- 
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Dave Haynie    {caip,ihnp4,allegra,seismo}!cbmvax!daveh

	"I gained nothing at all from Supreme Enlightenment, and
	 for that very reason it is called Supreme Enlightenment."
							-Gotama Buddha

	These opinions are my own, though for a small fee they be yours too.
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