what is Voltage Swing - Voltage swing is the change in voltage to signify a logic bit ( 0 to1 or 1 to 0). It must meet DRAM SSTL voltage specifications. The low minimum specified voltage is VIL and the high is VIH. The signals in the eye diagram have to "swing" between these levels for the transitions to be valid. The eye diagram also show any overshoot or undershoot related the voltage swing.