def METHOD_NAME(self):
    """add tri gate to the array """
    self.tri_inst = {}
    for i in range(0,self.columns,self.words_per_row):
        name = "Xtri_gate{0}".format(i)
        self.tri_inst[i]=self.add_inst(name=name,
                                       mod=self.tri)
        index = int(i/self.words_per_row)
        self.connect_inst(["in_{0}".format(index),
                           "out_{0}".format(index),
                           "en", "en_bar", "vdd", "gnd"])