7 Jan
2009
7 Jan
'09
1:25 p.m.
On 07/01/2009 15:46, Bob Armstrong wrote:
Forgiven :-)
Actually it *is* on the card, just not in the form you might expect.
All I/O page access on a QBus is controlled by a separate signal called
BBS7 (Bus Bank Select 7) and I/O page devices respond to that being
asserted, not by actually decoding the upper address bits (which they
ignore). However, a consequence of that is that cards which do decode
18 address bits (like an MSV11-D) is that they may respond to addresses
which are in the I/O page in a 16-bit system -- in other words, a 64KB
(32KW) MSV11-D with a base address of 000000(8) responds to all
addresses from 000000(8) to 177777(8). It has a jumper to disable the
top page. Maybe you need to do that?
No, they don't need to be removed, but they should normally only be
installed for a quad CPU. They connect two fingers on the upper side of
section C to the corresponding fingers on the lower side.
Pete Turnbull
(pete at dunnington.plus.com) wrote:
No, that'll be a BA11-M ...
Oopss. Sorry. The issue is
not the number of address bits, which won't matter at all.
That's what I was hoping, but there's one thing I don't understand - the
LSI11 CPU only drives 16 address bits, but some of the option cards (e.g.
DLV11-E) and the MSV11 memory decode 18 address bits. It's not sufficient
to simply pull the upper two address bits to always be zeros or ones - the
upper two address bits have to be zeros (for the memories) when the CPU
outputs an address in the range 000000..157777, and ones (for the I/O cards)
when the CPU outputs an address from 160000..177777. It's not a difficult
problem, but where is the logic to do this? It's not on the LSI11 card,
since those extra address bits weren't even defined in the QBUS when this
card was made. It's that
your H9273 backplane is set up for an 11/23 and won't have
W2 and W3 inserted, but they need to be for a quad-height M7264 ...
Actually the BA11-N H9273 does have W2 and W3 installed - according to the
Microcomputers and Memories handbook, those are supposed to be installed if
the CPU is in slot one, and removed if there's no CPU (i.e. for an expansion
box). It doesn't actually say anything about which model CPU, but in any
case they are installed on mine. Do they need to be _removed_ for an M7264? So is W1 (installed) for that matter, which I think
controls the LTC.
Yes, that's right (and normal), though it should be removed in all but
the last box in a multi-box setup.
--
Pete Peter Turnbull
Network Manager
University of York