> If I understand this circuit correctly the PIC is holding itself up
> by its own bootsraps with no visible means of support - ie
> powering its own Vcc from port pins which draw power from
> Vcc which.........

> get the PIC to hold a port pin high to supply its own Vcc

The PIC gets Vcc through the switch to get it running. Not shown
is a separate port line that goes to Vcc to maintain it. The switch
lines aren't used to keep it alive, just to get it alive. But I think you
could still use tthe switch lines. Assuming a typical key press is
at least 300ms that gives plenty of time for the PIC to stabilise,
read the port to find out which key was pressed and then change
that line to an output to keep driving Vcc until it's done doing what
it's doing

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