PDP-11/84 Qbus slots for memory

Jerry Weiss jsw at ieee.org
Sun Jul 22 17:43:42 CDT 2018

On 7/22/18 12:54 PM, Noel Chiappa via cctalk wrote:
>      > From: Mark Matlock
>      > With the 11/83 the position of the memory board ... above the CPU uses
>      > PMI
> Yes, through the C-D interconnect; described in detail here:
>    http://gunkies.org/wiki/CD_interconnect#Use_by_PMI
> The 'above' is because the CD interconnect is not a true bus, it only
> interconnected pairs of slots.
>      > In the 11/84 the CPU is above the MSV11-JE memory
> The PMI is still on the CD connector in this machine, but the PMI is wired as
> a true bus on the backplane, allowing that ordering.
>      > there are 3 Bus slots in the 11/84 above the Unibus map board, would it
>      > be possible to put a dual width Q22 I/O board in the second memory slot
>      > (not the PMI side of the slot) and have it able to DMA into the
>      > MSV11-JE?
> It is speculated that this should be possible, but there are jumpers on the
> backplane you'd need to pull. See the writeup here:
>    http://gunkies.org/wiki/PDP-11/84#QBUS_slots
You might also need a change to the device handler.  For example in 
RT-11 to support the mapped window from 18bit to 22bit, the DU handler 
(for a UC07) uses extended memory subroutine $MPPHY ($MPPTR)  tell the 
controller what addresses to use.  $MPPHY uses Q.PAR, which is the 
relocation constant for the UMR (when present).

Since this I/O isn't going through the KTJ11-B the handler at minimum 
would need to modified to use $MPMEM (Q.MEM) instead, to supply (in 
conjunction with Q.BUFF) the physical address.


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