I don't know if this works for all the Dilog Qbus controllers, but..

>>>D/P/L 20088004 80000001
>>>D/P/W 20001F40 20

- the above two lines enable dma from Qbus to memory on the MicroVAXII
  (I don't know what the incantations are for other Qbus systems like the
   3500.)

>>>D/P/W xxxxxxxx 3FFF		where xxxxxxxx is the physical address of
				the board's SA (on a MicroVAXII with a first
				default disk controller, it's 2000146A I think)
>>>S 200
- for some reason the start address is 218 instead of 200 for a machine
  with a GPX colour display

Good luck with it, rick