27 Mar
2001
27 Mar
'01
1:30 p.m.
Now, how similar is the CPU to the 9825's CPU? If
it's the same
hybrid, then the I/O bus is reasonably-well documented, e.g. in the 98032
service manual.
According to the HPJournal article, it's similar but not identical. I
remember that it replaces an indirect bit on memory access with an
additional direct address bit, but I don't remember whether the article
says anything about electrical differences.
In the 9825, the I/O modules plug into a little
backplane with a ribbon
cable linking it to the rest of the machine (tape controller, CPU board,
KDP interface [1]) Since the backplane is just connectors, the pinout of
the ribbon cable is trivial to deduce. If that's what links to the
'monitor' in the 9845, then it should be possible to figure out what is
going on.
The 9845 does have the same I/O backplane, but I don't believe the
monitor connections are the same. The monitor sits on two 'legs', each
with a card edge connector; some of the alphanumeric display logic sits
in the main box under the left leg and connects to the rest on the left
side of the monitor, while the right side of the monitor holds the
(optional) bitmap memory and connects through the right leg. (The
alphanumeric display runs off a display list, not a rectangular buffer;
the I/O processor alternately fills two single-line buffers, and from a
quick glance at the block diagram, *those* are in the main box.) It
might not actually be too difficult to figure things out -- at least
what the turn-on fixture is -- but I don't have time right now to look
at it or read the whole manual.
--
Kevin Schoedel
schoedel(a)kw.igs.net