1)how can I modify 'startup' so that after entering PDM my variables do not lose their contents. 2)Also, I do not think I want to come out of PDM through reset but through an External interrupt INT0...is that the same as reset?
1) depends on your compiler, if keil, modify startup.a51, what you need do is slear once you look at it.
2) no, not the same, SFRs and variables preserved on interrupts. Many '51 deruvatives will only leave power-down by reset., i think (do verify) the '932 can get out on int0.

Erik