An apparatus includes: a master die; one or more slave dies; a ZQ resister between a first node and a second node coupled to a voltage terminal; a ZQ pad coupled to each of the first node of the ZQ resister, the master die and the one or more slave dies; and a calibration channel electrically coupling the master die and the one or more slave dies, the calibration channel configured to communicate signals between the master die and the one or more slave dies for coordinating access to the ZQ pad across the master die and the one or more slave dies.