PDP-11/84 Qbus slots for memory

Mark Matlock mark at matlockfamily.com
Sun Jul 22 07:47:56 CDT 2018

   The PDP-11/84 uses the M8190 CPU that is also used in a PDP-11/83. The 11/83 and 11/84 use PMI
Memory but the 11/83 also can use Q22 memory. With the 11/83 the position of the memory board (assuming
one is using the MSV11-JD or JE) above the CPU uses PMI and below the CPU in the backplane uses 
Q22. In the 11/84 the CPU is above the MSV11-JE memory but the CPU only uses PMI to talk to memory.
diagrams in the Unibus processor handbook indicate that the M8191 Unibus map board only communicates
through the PMI bus to both memory and to the CPU.

   Now my question is, 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? 

   If so then something like an Emulex UC07 and a SCSI2SD card could make a cost effective disk solution, 
since Unibus SCSI controllers are so expensive.


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