There is everywhere in the manual that port's have pull-up's, but what are
the values of the pull-up's in ports 1, 2 and 3 ?
You can optimise the value of the pull ups depending on the speed and power
requirements. 10kOhms is a good start. The maximum value is determined by the
leakage current and the noise margin to the positive rail or the maximum
risetime required combined with the line capacitance.
10kOhm usually satisfies both of these requirements.