28 Sep
2014
28 Sep
'14
11:34 p.m.
A lot of DEC memory of that era used separate parity boards. The M7259 and
the M7850 were both used for these.
It is common to have parity memory with no parity board. I don't remember
if there are any jumpers on the memory boards, but if you haven't checked
it might be worth while to look into.
DEC used to get carried away with jumpers, the 11/40 is a good example. You
can add an option of take one out and have to change a half dozen jumpers
on cpu boards.
On Mon, Sep 29, 2014 at 1:10 AM, Josh Dersch <derschjo at gmail.com> wrote:
On 9/27/2014 9:59 PM, Josh Dersch wrote:
On 9/27/2014 2:11 PM, Tony Duell wrote:
OK -- I spent a bit of time looking at the schematics for the H215 in
pursuit of my crazy plan and I was initially puzzled -- it didn't actually
look like there's hardware on the board (or the associated control/driver
logic) to actually address 18 bits. I saw the sense/inhibit lines for bit
P0 and P1 outlined, but there are no associated diodes on the X/Y switches.
After reading through a few different sets of documentation, it turns out
that these lines are driven by an optional parity controller, the M7259
(which, when combined with an H215, G109 and G231 makes an MM11-LP). The
M7259 apparently contains the diodes "missing" from the H215 to drive the
parity lines. Of course I don't have this board in my 11/05, which makes
me wonder why it has an 18-bit core plane to begin with...
At any rate -- I can't find a schematic for the M7259, which would help
narrow down which edge connector pins on the H215 are used for the X/Y
selectors for the additional parity bits. I could do this by process of
elimination, but just in case someone happens to have this scanned, I
figured I'd ask...
Thanks,
Josh
Incidneatlly, no matter what it says on the cover
over the core mat, you
can take it off quite easily without damage. Just don't drop it on the
corse.
If it is the core address wire in the mat, you may have big problems.
Some of these mats had the cores cast onto the array of wires, no
pre-made cores that were threaded with the wires. In which case,
replacing the wire might be impossible.
My first throught was 'have a go anyway. If you wreck the board, well, it
doesn't work now'. And then I thoguth that no, you should treat it with
care. Even if you don't have the skill to fix it now, you might do so i
nthe future. Or somebody else might have a go. In any case, you don't
want ot make thigns worse.
I do have a semi-crazy idea: The H214 I have is 8Kx18 bits (i.e.
parity). If I were to disable parity on the control boards and reroute one
of the parity-related lines for this damaged section, maybe I could get a
complete 8Kx16?
I'll have to do a bit more research...
- Josh
-tony