Okay, I'm paranoid. I was going to use the micro to drive LEDs, but added a buffer when reading the U/G footnote about 12ma/48ma limitations relative to CMOS current impacting supply voltage. Now I want to play with a touch screen. First - and probably unimportant - is that the (otherwise excellent) app note for 4/8 wire touch interface states that 'any' Touch International panel should work. I looked there to get a pinout, and there are quite a few different 8-wire pinout flavors! So I'll need to work backwards from the code to get pinouts. Might have been clearer to indicate pinouts may not be 1-for-1.
My main concern is with current. Trying to nail down a 'typical' touch panel resistance has proved futile. The best I can do is "a few hundred ohms". If I use a GPIO to "drive" Y+ or X+, and another to ground Y- or X-, what's my current? From the simple formula, it would seem that a 200 ohm panel driven at 3.3v would require 16.5ma. And, I'm not sure how low the resistance can go depending on where the panel is touched. Am I worrying unnecessarily? Does the internal architecture obviate my concerns? If so, then why is any limit not applies to simple source/sink operations? Thanks in advance for any data you might provide to quell my anxiety and allow me to continue moving forward with initial design.