>
>Take a look at the following app note.  "Random" is relative; it depends
>on the number of bits in the shift register before the pattern repeats.

It's not random at all.
It's completely and absolutely predictable.
Radioactive decay is random.
Although it's gaussian in large groups, the time between decays is totally 
unpredictable.
OTOH, if I know the register configuration (tap points) and what state it 
is now, or what state it was at any time previous, then I can predict the 
next state exactly.

The interesting thing is that if you only look at a small subset of the 
bits, then it appears random. If the register is long enough, and it 
doesn't take that much, it's repeat time can exceed the age of the universe.

This makes it very useful for secure radio links.

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