PDP-11 Memory

[Bill Gunshannon]

On 1/11/19 2:32 PM, Noel Chiappa via cctalk wrote:
>      > From: Allison Parent
> 
>      > Most Probable cause is interrupt grant is broken.
> 
> The only -11 that complains if the grant chain is broken that I know of is
> the /34 (maybe the /04 too). I certainly have a QBUS chassis right next to my
> workstation here that i) has a bunch of empty slots, and ii) works fine, as
> long as there are no empty slots between the CPU and the devices.
> 
> Also, IIRC he said it works with 3 cards plugged in, but not 4; how can
> plugging a card _in_ cause grant problems?
> 
>      > For most microspheres backplanes the first three slots are different
>      > than remaining.
> 
> That might be worth checking into. I'm not familiar with the second box
> he's using, so can't help there.

MicroPDP box has first three slots A-B-C-D to support PMI
memory and the rest are serpentine A-B.

Even giving a bus grant problem, I can't see that causing a CSR
error.  I will probably have to dig out another box this weekend
just to be sure there isn't a problem with the backplane.


bill