Thanks for the answer Charles,

I tried your suggestions and it does not work. The tristate of the pins is setting ok, the problem is when I try to set output states in sequential lines, for example:

PORTC.0 = 1
PORTC.1 = 1
PORTC.2 = 1
PORTC.3 = 1

This sequence just highs the pin PORTC.3, the remaining three pins states Low.