Cross-talk square-wave?

[Noel Chiappa]

    > From: Eugene (W2HX)

    > I am still not convinced it is coupling at all. ... I just don't think
    > you can get square waves from square waves.  ...
    > it is even harder to believe one could successfully couple a square
    > wave onto such a transmission line unless the signal is actually being
    > asserted on the line at a low impedance ...
    > Looking at this picture ... this shows exactly what I would expect to
    > see with cross talk the little glitches on the CS line that correspond
    > to edges on the clock signal.

Exactly. That sort of cross-talk we understand (and have seen before). But
a square wave? How can that be? That was the motivation for my original post.

It's not super-critical to understand, because like I said, this is on a
pre-prototype, and the actual unit will be arranged nothing like this (no
cable, etc, etc), so we're just going to fix this with whatever kludge makes
it go away, so we can focus on the things we really do need to work on.

But we'd still like to understand what is happening here, and how. Could
cross-talk (of whatever form, inductive or capacitive) do this, or does this
more or less have to be signal leakage (on the board at one end, or the
other) somehow?

	Noel