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From: larry@hpfclg.UUCP (larry)
Newsgroups: net.micro.68k
Subject: upper 8 bits on *68020*
Message-ID: <33000001@hpfclg.UUCP>
Date: Tue, 26-Mar-85 14:05:00 EST
Article-I.D.: hpfclg.33000001
Posted: Tue Mar 26 14:05:00 1985
Date-Received: Mon, 1-Apr-85 03:47:45 EST
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 10
Nf-ID: #N:hpfclg:33000001:000:493
Nf-From: hpfclg!larry    Mar 26 11:05:00 1985

Using the top 8 bits of the program counter of the 68020 is not
as good a thing to do as on the 68000.  It will work if you just
don't connect those address lines, but, if I'm not mistaken
(it's happened before), the on chip cache uses all 32 bits of the
address.  If the upper 8 bits aren't really used for address,
there will be fewer cache hits, and lower performance.  How much
lower, of course, depends on how often those upper 8 bits change.

Larry Fenske
{hplabs, ihnp4}!hpfcla!larry-f