Of course, you must make sure that the software always drives the parallel pins to the same state at the same time. Otherwise you would have contention between the output drivers in the PIC, which at the very least will waste current heating up the part, and may permanently damage it.
Note that in addition to the per-pin output drive spec, there is also a per-port spec. This means that there is generally no benefit to tying very many port lines together. For example, the PIC16C5x family is spec'd for a maximum current sink per port pin of 25 mA, and a maximum current sink for a whole port of 50 mA.
Last updated September 9, 1995
Copyright 1995 Eric Smith