PDP-11 Memory

[Bill Gunshannon]

On 1/11/19 3:41 PM, allison via cctalk wrote:
> 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).

Not only that, it will kill the RL11.

> 
> 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).
> 

At this point I am going with your comment about bus grant.
I don't know why but that seems to be the likely culprit.

More to follow if I get this working.

bill