PDP-11 addressing question and a model round-up

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Mon Feb 14 18:38:21 2005

On Feb 14 2005, 12:59, Eric Smith wrote:
> Pete Turnbull wrote:
> > However, early versions of
> > the KDF11-A had 18-bit ODT while later versions, and all KDF11-Bs,
> > 22-bit ODT. All would still happily cope with 22-bit memory under
> > control of the MMU (as far as I remember -- someone please correct
> > if I'm mistaken), providing they are in a 22-bit backplane.
> Are you sure that there was a difference in the ODT? I thought the
> ODT was the same in all F11 chipsets, and the difference was purely
> a matter of whether the KTF11 MMU was installed, and whether the
> wired the top four address lines to the bus.

No, I'm *fairly* sure there was a difference in the ODT. Perhaps
Sellam can tell us for a change; if he has an 11/23 (KDF11-A) with
18-bit ODT (his MXV21 responds to 777170) and also an 11/23-plus
(KDF11-B) with 22-bit ODT (his MXV21 responds to 17777170 but not to
777170) he can tell. Otherwise I'll have to go and do a bit of digging
to see what CPUs I've got, but I think all the KDF11s I have at the
moment are Rev.C KDF11-As.

> Hmmm... makes me wonder whether ODT on a system without the MMU
> can access physical memory above the 28KW mark. I may have to try

That I can test... except I don't have time right now to dig out a card
and plug it in. Sigh. Maybe over Easter I should tidy up the workshop
enough to at least get in the door ;-)

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Mon Feb 14 2005 - 18:38:21 GMT

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