If you use only external program memory, you have always heavy activity on AD0..7, so no resistors needed.

But if you use only external memory mapped I/O, the data pins can float for longer time, which should be avoided. E.g. I inserted the following instruction on the end of every routine, which access external memory peripherals:

P0 = 0;

Then the bus was pulled low all times until the next access.


Its also recommended, if you never use P0 on your application to place this instruction inside the main() at first.


Peter