The present application relates to a system and a method for determining relative positions slave units along a stub bus with at least a power line and a ground line. Each slave unit is operable in different power modes, which are differentiated by effective resistances between the power and ground lines. A reference voltage potential drop is determined for each slave unit while the slave units are operating in a first power mode. A positioning voltage potential drop is determined for one or more slave units while a selected slave unit is operating in a second power mode. Relative positions of the slave units are determined based on the relative voltage potential drops obtained from the reference and positioning voltage potential drops.