23 Feb
2006
23 Feb
'06
1:54 p.m.
The only problem with SPC slots is they are 18b UNIBUS
only. This will
work on 256KB 18b machines, but is a sticky problem on 4MB 22b machines,
since you need to go thru the UNIBUS map to get to all of memory.
For an 11/44, you could do just a dual slot card that goes in a memory
slot (which has 22b address available) and an SPC slot (to get the DMA
lines) but this would be a hex card. To read/write memory, you would
need to be a 22b DMA device, which I'm not sure the 11/44 can handle
AFAIK there are no 22 bit DAM devices on the Unibus. The processor
(either the MMU or the Unibus Map) always drives the memory address lines
-- DMA addresses from the Unibus are translated (via the Unibus Map) to
the correct 22 bit address for memory
I don't think even an 18 bit could work on a 11/44. You could use DMA
cycles to access memory, but since your (18 bit) address would go through
the Unibus Map, you'd not actually know where you were accessing.
-tony