Hi Bob_walker,
Actually, SWM is defined the according internal block interface to the detail chip pin, PIO0_0 to PIO0_28.
What do you mean:unbonded I/O?
Do you mean? Take an example:

This pin don't have PIO0_20, but if you use SWM connect the internal block, various block, no external pin, but the internal different block will be connected.
This picture may help you to understand it.

Wish it helps you!
Have a great day,
Kerry
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