30 Mar
2006
30 Mar
'06
10:16 p.m.
On 3/31/06, Jay West <jwest at classiccmp.org> wrote:
Here's where I'm trying to start. I was
looking at some of the code on this
website, hints for troubleshooting a dead PDP11. It's at:
http://www.psych.usyd.edu.au/pdp-11/hints.html
I enter and run the Line Time Clock Interrupt test from that webpage, and
the system halts at location 4. How on earth? Does the 11/45 have some
interrupts to specific locations for things like power fail or something?
Should a unexpected trap to location 4 mean something special to me? Here is
the section from that website reproduced below:
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.
-ethan