1. A method of generating neuron spiking pulses in a neuromorphic system, comprising: floating one or more selected bit lines connected to target cells, the target cells having a first state, from among a plurality of memory cells arranged at intersections of a plurality of word lines and a plurality of bit lines; and stepwisely increasing voltages applied to unselected word lines connected to unselected cells, the unselected cells having a second state, from among memory cells connected to the one or more selected bit lines other than the target cells having the first state.