PDP-11 Memory

[allison]

On 01/11/2019 02:55 PM, Bill Gunshannon via cctalk wrote:
> On 1/11/19 2:25 PM, Allison Parent via cctalk wrote:
>> Most Probable cause is interrupt grant is broken.  For most microspheres backplanes the first three slots are different than remaining.
> Yes, that's true.  But the problem doesn't occur until the 5th slot.
> And a quick look at the C-D edges of the board shows that the BUS
> Grant lines are jumpered. So the 2 A-B slots should pass the grants
> just fine. I saw  no mention about these not working in A-B/A-B
> backplanes.  The only mention the docs make at all is that the
> only lines used on C-D slots is power.
>
> bill
>
That is generally true... however there were more than a few odd backplanes
including a few that were wired for Core and some design to suit a
different
memory and incompatible (smoke releasing!).  Others are unique as the RL11
two board set require a CD backplane slot pair (will not work if ABAB).

You need to look at the backplane and find out what one it is.

I have a few boxes I got without a backplane at all and as a result they
have
what I find was most useful and very non standard.

The CSR complaint is because if you talk to the board and don't get a
int vector
or can't set a working one (floating)  the CSR is broke.  This is a
behavior that
is much different from unibus.  It also happens if an expected CSR is
non standard
for nominal drivers.  An example is my 11/73 as it has 2 RQDX3 so one
has to be
at a new and unusual CSR same for the second DLV11J serial.  Some memory
(parity or ECC) also have CSRs and if they interupt and the drive is not
there
I've heard havoc ensues (of all my memory on hand none have that).

Irs a side effect of the Q bus starting in the 70s (LSI-11) and
continuing with
some evolution though the 90s (11/83 and 11/9x).

Allison