 In these configurations, the relocated resistors make it possible to light multiple LEDs at the same time row-by-row, instead of requiring that they be lit individually.The row current capacity could be boosted by an NPN emitter follower instead of the typically much weaker I/O pin.Because only a single set of LEDs, all having a common anode or cathode, can be lit simultaneously without turning on unintended LEDs, Charlieplexing requires frequent output changes, through a method known as multiplexing.