31 Mar
2008
31 Mar
'08
3:09 p.m.
I'd have to look up the RL11 to know if it could
be used in a 22 bit
machine, but if so, it'd be 17777404 and 17777400.
It can't. It's a Unibus device, and the Unibus only has 18 address lines.
On Unibus machines with 22 bit memory addressing (11/44, 11/70, etc)
there's a second 'MMU' -- the Unibus Map -- that translates 18 bit DMA
addresses from peripherals into 22 it memory addresses. To access
peripheral control registers, the 18 bit Unibus 'space' is mapped into
the top of the 22 bit address space produced from the 16 bit
prgram-generated address by the normal MMU.
-tony