30 Mar
2006
30 Mar
'06
11:21 p.m.
On Mar 31 2006, 18:16, Ethan Dicks wrote:
Yes... the lowest trap vectors on _all_ PDP-11s are
fixed and mean
something special when you hit them. I don't have a reference right
in front of me (should be in all of the small computer handbooks),
but
on a different spot on that page, it mentions this...
Location Contents Opcode Comment
000004 000006 Bus Error trap
000006 000000 halt
000010 000012 Reserved
instruction trap
000012 000000 halt
000024 000026 Power fail trap
000026 000000 halt
... so if you really are halting at 000004, sounds like a bus error.
Perhaps the code you toggled in can't find an I/O register it's
expecting.
No, if you have set up the standard trap catcher, and you halt at 4, it
loaded the vector from 0, executed the HALT instruction at 2, and the
PC contains 4 by the time it stops or returns to ODT.
--
Pete Peter Turnbull
Network Manager
University of York