SPICE “V” element with “PWL” option which is expressed in related time step generates a PWL(Piece-wise Linear) wave signal.
The syntax of “PWL” which is expressed in related time step is as follows.
Berkeley SPICE2, HSpice, PSpice, XSpice, LTspice
Vxxx n+ n- PWL time0 voltage0 +time1 voltage1 +time2 voltage2 …
You can use related time step expression to place “+” ahead of time value.
V001 N001 0 PWL 0,0 TSTART,0 +10n,5 +480n,5 +10n,0
.PARAM TSTART list 10m 20m 30m
The symbol of LTspice’s “V” element with “PWL” option which is expressd in related time step option is “voltage” which is in “C:\Users\Username\Documents\LTspiceXVII\lib\sym” directory. If you want to set the parameters of that by GUI, click “Advanced” button on “Component” menu window and check “PWL(t1 v1 t2 v2…)” or “PWL FILE” in “Functions” setting.