> What I have thought is having 2 analog sources, ground, and
> digital signal on each pin.  For switching between them, I
> have thought on an analog multiplexer (4->1), and then a
> switching matrix is not required.

Take a look at Needham's Electronics (www.needhams.com)
line of device programmers for another solution.

They feed the various signals to different pins for various
parts using small jumper boards.  This way you have a solid
Vcc, ground, etc.  And you can reduce the number of expensive
analog drivers to the minimum number needed; the jumper board
routes them to the right pins based on the device or family
being programmed (or tested).
                                                Lee Jones

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