[Simh] PDP-11 -- MFPI, etc, with memory mgmt off

[dave porter]

I hope you'll excuse a non-SIMH question on this list.

Over in the retrocomputing forum on Stack Exchange,
I'm involved in a conversation that says that the 
11/73 move to/from previous-mode space instructions
MTPI, MTPD, MFPI, MFPD, will, when the MMU is
not enabled, use the previous-mode bits from the
PS directly as bits 16,17 of the physical address.

I've never heard of such a thing and I cannot find
anything written that really says what these 
instructions do when running unmapped.

Anyone know about this?  (Mr. Supnik?)

If I shouldn't have asked this non-SIMH question
on this list, just say so and I won't do it again.
Thanks.