I also think that unless you really need to have all I/O port pins of your processor set as low outputs then it is not necessary to start out the first thing in the program and set P0,P1,P2, and P3 all to zeros. Out of reset these ports come up set to all ones so that all the pins are in their "input" mode.

Michael.

PS....At this point I so not really know where to guide you. Maybe after you have read some more and experimented with your prototype a bit maybe you will see or come across something more to come and talk about.

MJK