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From: pl@etana.tut.fi (Lehtinen Pertti)
Newsgroups: alt.sources.amiga,comp.sys.amiga,comp.sys.amiga.tech
Subject: Re: replacing the 68000 by a 68070 - is it possible
Message-ID: <1990Aug14.073539.4102@funet.fi>
Date: 14 Aug 90 07:35:39 GMT
References: <453@krabat.marco.UUCP>
Sender: news@funet.fi (#News )
Organization: Finnish University and Research Network FUNET
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From article <453@krabat.marco.UUCP>, by helmut@marco.UUCP (Helmut Raiger):
> Hi,
> does anybody know wether the Amiga 500 runs with the 68000 replaced by
> an 68070 (I know, that the 68070 does not have an synchronous bus interface - 
> E, VPA and VMA missing). Can the Amiga firmware support this chip? The short
> exception format is like the one of the 68010, but the long one is different.
> 	thanks in advance
> 		helmut (helmut@marco.de)
>

	SCC68070 (<- Philips ID) is almost same as 68000 on software
	(no MOVE from CCR, move from SR wont trap).

	From 68010 comes virtual memory support (bus faults handled ok).

	This drops it nastily between those two (trap test says 68000, but
	stack frame differs).

	Worse problem is on hardware side.

	Amiga uses all interrupt levels as 680X0 allows, but on
	68070 all levels aren't available (one misses due different decoding),
	and this causes quite a lot problems, as we should redirect
	this somehow to correct vector, I think NMI could be used for this,
	but it is hard to say without trying.

	I afraid, that it won't work.

--
pl@tut.fi				! All opinions expressed above are
Pertti Lehtinen				! purely offending and in subject
Tampere University of Technology	! to change without any further
Software Systems Laboratory		! notice