On Apr 22, 16:08, Philip.Belben_at_powertech.co.uk wrote:
> Subject: Re[2]: PDP 11/23 help needed
> Seth and Pete were discussing the PDP11-23...
>
> >> 2) Same as above, but for the M8044-DB boards. I could put one
> >> of these in with the M8047's to get a full 64Kword of RAM, yes?
> >> Does anyone know what the DIP-switch settings for these boards
> >> are?
> >
> > Yes, but I'm not sure why you say "full" and 64Kword" together :-)
> > 32KW (64KB) is the limit for 16-bit addressing, or 128KW (256KB) for 18-bit
> > addressing. Ignoring the I/O page, that is.
>
> Um... Am I way out here? Doesn't the 23 support 22 bit addressing? And
> I never before heard of a 16 bit Qbus! ISTRT the F11 processor is
> settable between 18 and 22 bit (128KW, 256KB and 2MW, 4MB respectively).
> The 18 bit setting is used in the 23 on 18 bit Qbuses and in the 24 on
> unibuses. The 22 bit setting is used on 22 bit Qbuses, but you need
> extra hardware to use it in the 24 (i.e. on unibus).
An 11/23 only supports 18/22-bit addressing if it has the MMU chip fitted,
which
almost all do, though it was, strictly speaking, an option (at least, for most
of the 23's life).
Early KDF11-A's (Rev.A) only support 18-bit, most (Rev.C) support 22-bit
addressing -- iff they have the MMU. Otherwise, they can only access 16-bits
of
address space. I don't recall any setting to change that, you just only get 18
bits in an 18-bit backplane. If you try to access beyond that range, you get a
bus error. ISTR that the ODT still works (always 18-bit) without the MMU,
though. I can't easily check as the only one I have running ATM is a 22-bit
system.
A number of KDF11-A's were fitted to 11/03's as upgrades, and those had 18-bit
backplanes. The 11/03, however, only had a 16-bit address range, as did early
core, MOS RAM, and ROM boards. I wasn't referring to the bus as 16-bit, but to
the address range.
For slightly different reasons, you can't use an MSV11-D (or several other
options) in a 22-bit system. It will fit in the backplane, and work fine, but
it effectively turns the whole system into 18-bit, because it doesn't decode
BAL18-21, and therefore responds to sixteen blocks of addresses.
For similar reasons, the RKV11-D is not often used in 18-bit or 22-bit systems,
since it can only perform DMA with 16-bit addressing (you can access the
registers in an 18- or 22-bit system, of course, because it responds to the
BBS7 signal). There are lots of other I/O options with similar restrictions.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
Received on Wed Apr 22 1998 - 11:07:56 BST