27 Jul
2011
27 Jul
'11
1:37 p.m.
How did you
connect your scope? Looks more like a ground problem with your
measurement setup.
This could be the problem. I don't have an isolating
transformer. GND
of the scope and GND of the PDP-11 are connected to earth of the mains
plug. Because of this I connected both to the same power strip. I did
_not_ connect the GND clip of the probe to GND of the PDP-11. If I had done this, I would have created a ground loop. This,
of course, _will_
create problems. Without connecting the GND clip of the probe my
reference point was in the power strip.
I can assure you a groudn loop -- a small omne like you'll have here --
will not cause problems withterse sorts of signals. Try again with the
'scope ground led connected.
-tony