We are using XTAL0 as a gpio input(alt1), configured with an internal pullup (PCR=0x103), and are seeing this input regularly drop about a volt at the clock frequency when driven high. It's a weird behavior that we can't seem to run down. Has anyone here happened to of used XTAL0 as an INPUT instead of an output, and if so, have you seen any similar behavior? We do have an external clock input as well. I am leaning towards board layout/external hardware issues at this point, but hope to rule out the fact that the pin it XTAL0 as a possible source. The Port Control Register is not changing and the micro is not resetting.
Thanks for any help.