Diff between 11/20 and 11/45?

Dave Horsfall dave at fgh.geac.com.au
Wed Sep 8 16:29:16 AEST 1999

On Tue, 7 Sep 1999, Steven M. Schultz wrote:

> > 	MOV SP, -(SP)		MOV SP, R0
> > 	MOV (SP), R0		MOV R0, -(SP)
> 	Ah, thank you for bringing that memory back to the front of the brain!
> 	If R0 is available for that then yes indeed that'll do the trick very
> 	nicely.

Yep, I remember that now!  Often thought it was odd, but it worked
on all platforms.

The convention was that R0/1 were scratch (used to return results)
and R2/3/4 had to be saved (they were the caller's first three register
variables).  R5 was used as a frame pointer (?) and R6/7 you know
better as SP/PC.

> 	The 11/45 (and 70) behave as "expected" as do the KDJ-11 systems
> 	(11/73, etc) so unless a person had an 11/40 (or a /20) around it
> 	would be fairly easy to get bit by the "feature".

We had 40s, and used to dream of owning a 70...  I learned a lot about
porting Edition 6 to the /23, /60, etc.

> 	When it comes time for MMU "features" I know of one difference between
> 	the KDJ-11 and the other members that had an MMU (11/44, /70, etc). Was
> 	fun tracking it down but not something I'd want to do again ;)

Do you recall the PC-board hack on the sep-ID machines that changed
the MFPI instruction to do something that was expressly prohibited?
Something about allowing a user program to access something else, for
some obscure hack or other...

Dave Horsfall VK2KFU  dave at geac.com.au  Ph: +61 2 9978-7493 Fx: +61 2 9978-7422
Geac Computers P/L (FGH Division) 2/57 Christie St, St Leonards 2065, Australia

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