all babble about standard '51 ports being "input" ot "output" is bull...., baloney, false, incorrect, erroneous and has no purpose but to confuse the novice.

A standard '51 port is neither input nor output it is quasi-bidirectional.

If it need be spelled out
mov a,Px will read the voltage on a port pin which, if the port latch is set high can be pulled low by external forces due to the port being quasi-bidirectional. If the pin is set low, the "strength" of the force (see the architecture) holding it low is so that, if an external force try to pull it high, destruction will result.

will I have to define each pin of port P1 independently as:
P1.0 = 1
P1.1 = 1
and so on.
why on earth would that make a difference.

BIBLE TIME Read all about it.

DO NOTE: some modern derivatives have "port configuration SFRs, the above does not necessarily apply to them.

Erik

here are the links to "the bible"
Chapter 1
http://www.semiconductors.philips.com/acrobat/v...ARCH_1.pdf

chapter 2
http://www.semiconductors.philips.com/acrobat/v...UIDE_1.pdf


chapter 3
http://www.semiconductors.philips.com/acrobat/v...WARE_1.pdf