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From: steveg@hammer.UUCP (Steve Glaser)
Newsgroups: net.micro.16k
Subject: Re: Address bit 24
Message-ID: <1414@hammer.UUCP>
Date: Mon, 29-Jul-85 19:04:52 EDT
Article-I.D.: hammer.1414
Posted: Mon Jul 29 19:04:52 1985
Date-Received: Thu, 1-Aug-85 21:43:46 EDT
References: <128@prime.UUCP>
Reply-To: steveg@hammer.UUCP (Steve Glaser)
Distribution: net
Organization: Tektronix, Wilsonville OR
Lines: 25
Summary: 

In article <128@prime.UUCP> davel@prime.UUCP (David Lounsbury) writes:

> Has anyone done a design using address bit 24 from the 32082 MMU?
> National has some vague suggestions about ICEs, but I'm wondering
> about using this bit as part of the physical address.  Any thoughts
> or suggestions are appreciated.

It works just like another address bit.  I understand that Sequent use
it exactly that way.  They support 28(?) Mbytes of memory (32M less some
I/O space).

We use it to enable our address expansion hardware (Tektronix 6200
series workstations) - local memory gets "simple" 24 bit addresses, but
the main system bus is 32 bit addresses requiring additional hardware
to generate.  If you want to go out on the system bus, kick A31 on and
you can generate a full 32 bit address.  We went with a 32 bit main bus
so we don't have to redo things down the road.

National data books refer to A31 (aka A24) as "AS" (Address Space) and
intended to have it used for selecting emulated memory or real memory
when doing In Circuit Emulation.  To my knowledge nobody uses it for
that purpose (including the National ICE products).

	Steve Glaser
	Tektronix Inc.